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July 10, 2007




Hello, Lynn,

There are some specialists who feel that heartworm positive dogs are more likely to experience ill effects with Interceptor than with Heartgard (a different drug).

I personally have not seen reactions with it, but some people have, and this may be part of your problem.

The Snap Test is pretty specific, in that it is unlikely to react to things other than the protein from the adult female heartworm reproductive tract.

Sensitivity refers to how many worms you would have to have present in order for the test to pick it up. This type of test (Snap, Abaxis, Witness, other "chair-side" tests) can give false negatives if fewer than four adult female worms are present.

A second Snap test may not tell you what you want to know. If positive and there WERE some type of cross-reaction (non-specific) , it might be the same thing. If negative, it might mean that you just have very few worms and were lucky to find them the first time.

In a case where there is uncertainty in our own lab, we always send a new sample out to an outside reference lab, like Antech.

If there are very few heartworms, most dogs have disease only in the pulmonary arteries, not in the heart. However, there is no good way to count the worms unless the dog dies and you cut him open.

If there are very few or no worms present, then the enlarged heart is probably due to something else, and could be worked up separately. An echocardiogram (ultrasound exam) can give you better information about the heart function than just an X-ray and physical exam.

Since I have not seen your dog or its circumstances, I can only give general information. You really need to discuss this with your veterinarian.

Best wishes.


Hi. I am confused about treatment for a very small rescued Brussels Griffon who is heartworm positive. She is young but very lethargic. The x-rays show a somewhat enlarged heart and pulmonary edema so my vet wants to use Immiticide. We are doing a month of doxy along with lasix and enalapril in the meantime. The rescue vet (without doing bloodwork or x-rays) says she's too small for the shots and should do doxy and Heartguard only because of her size (6.5 lbs.)

Does a small size increase a dog's risk? I'm obviously very concerned about making the wrong decision here. It didn't take this little girl long to be a very important part of our family. Thanks for any information.


Hello, Holly,

Very small dogs don't have much room for the dead heartworms to occupy. Three worms takes up a lot more of their pulmonary artery space than three worms in a German Shepherd Dog. They are indeed more likely to suffer complications from the breakup of the dead worms.

HOWEVER, they are also more likely to suffer illness with a small number of worms, for the same reason. Thus, I feel they should be treated.

The problem with just leaving the dog on Heartgard is that eventually, the heartworms present will die of old age. When this happens, the complications will be similar to those that would occur if you killed them with the treatment.

The difference is, with the treatment, you are doing everything possible to minimize the complications, and you also know when they will occur. Thus you can be watching the dog more closely and restricting its activity during this time.

You can't do that for the rest of the dog's life.

It sounds to me like your veterinarian is proceeding appropriately. I cannot give specific advice, as I have not seen your dog.

Discuss your concerns with your veterinarian.

Good luck.


Thank you so much for putting this info up.

Today I just found out that my dog Jewel (a German Shepard/Pit Bull mix) has heart worms. This has come as a hard blow for me.

To make a long story short: she is 3 years old, we got her as a puppy and have always had her on prevention until last year sometime (got busy). It tears my heart to know that it is my fault.

I don't want her to go through the pain, and knowing that other problems could come up makes me feel even worse. Also, she isn't too active, but every time she sees me she gets very exited (jumping around and everything). She is an all-the-time-outside-dog, so I can't watch her 24/7. But the main thing is, we can't pay for the treatment, and/or the other things that would happen. I am so sick over this and have cried for hours.
Would be be worth it to get a second opinion? (we have been going to this vet hospital for years, though it was a different vet) or should we really consider putting her down? I know that that isn't the best option, but at the moment I can't see any other way to keep her from being in pain.


Hello, Beth,

Not having seen your dog, it's hard for me to give you specific advice.

We have several patients whose owners are not able to do the treatment right away. We put those patients on Heartgard. This will keep them from getting many more heartworms, and is unlikely to cause a problem. At least you are "holding the line".

While it would be better to clear the dog, I wouldn't have problems with holding the line until you are able to. If the dog feels okay, I cannot see any reason to euthanize at this point.

We treat plenty of dogs who are outside while their owners go to work. Certainly 24-hour observation would be ideal, but it is almost never the case.

It sounds like there is some failure to communicate here, either from the veterinarian to you, or from you to me.

Please contact your veterinary hospital and ask to see your regular doctor. Share your concerns with him/her.

Best wishes.


This is a great site. Helps to know that others are going through this. We adopted a male lab in January this year. When we took him to the vet, we found out that not only did he test HW+, but his previous owner knew that he tested HW+ in June 2009 and did nothing. Maddening.

Here's our update: we treated the 4 weeks of doxycycline to kill the wolfbachia. We also did a shot of invermectin. We did the first immiticide shot in February. Rather than do the 2nd/3rd shots after 30 days, our vet chose to wait at least 3 months. We used monthly Heartguard in between the treatments.

Her line of thinking is that since the first Immiticide shot only kills adults, and the Heartguard only kills the microfalria, then we waited 3-4 months for any surviving baby heartworms to grow into adulthood. That way, all worms would be killed at all stages. Any worms that survived the 1st shot and made it to adulthood would be killed with the 2nd and 3rd shots.

Have you heard of this process before? The vet was at a conference the week before my appointment, and said that this was presented. It does stretch out the healing process, but seems to possibly have a higher percentage kill rate.

Anyway, we had shot #2 yesterday, and #3 this morning. I am just hoping and praying that we'll get through the next critical time period as the worms die off.

Any thoughts on this new 3-4 month approach? It makes sense to me, even if it does take more time.


Is doxycycline use recommended for dogs in all stages of heartworm? Is it now standard protocol to use this? My vet is not using it, and I'm just wondering in what situations it's not indicated.


The use of doxycycline is widespread. Is it the standard of care? I don't know that I could say that. It is recommended by the heartworm society researchers.

While some dogs do not tolerate it, having nausea and so forth, most do well with it. It inhibits the Wohlbachia micro-organism which is beneficial to the heartworm. This causes the heartworms to become weaker (and more easily killed), and smaller (less to dissolve afterward).

That being said, we treated thousands of dogs without it until the research recommending it was done.

In most cases, I believe that it cannot hurt and that it probably helps a little. I haven't done any controlled research, so I rely on those who have.

Thanks for reading and writing.


Hello, Barb,

The delay of three to four months would be important based on what time of year the dog is being treated. If you are already six months past the peak mosquito season, then everything that is going to develop is already developed.

In my area, that peak is July and August. If I diagnose and start treatment in January, there is little use in waiting three months for the next treatment.

If I am treating in September, then I certainly would finish treatment in January.

It is a function of when the dog's unprotected exposure to mosquitoes has taken place, and the time of year that treatment has begun.

Clear as mud?


I read about people using the terms "weak positive" antigen test result or "strong positive" antigen result. Could you explain what that means? Does it have any bearing on diagnostic plan or treatment plan?



Theoretically, that would indicate smaller or larger worm burdens.

In my opinion (and that of some bona fide experts, which I'm not), this is a qualitative test. Positive means yes, negative means no (or less than four adult female worms - false negative results can occur when worm burdens are this low).

I do not feel that you can make a meaningful determination of the number of worms from how "strong" the test result is. It's a color change, like a pregnancy test. "How pregnant are you?"

I make my estimate of worm burden based on the number of unprotected months of mosquito exposure, age of the dog, and whether there are any outward clinical signs of disease (as opposed to just a blood test result).

Chest X-rays will show changes in the pulmonary arteries, lungs and heart size.

For what it's worth, my opinion is that the usefulness of the blood test is just "yes or no".

If it turns up "yes" when I don't think it should, then we draw another blood sample and send it out to an outside reference lab to double-check.

Thanks for reading and writing.


Our newly adopted pup (a German Shepherd-- approximately 2 years of age and 55 lbs) just completed her Heartworm treatment two weeks ago, the day before we adopted her.

She is not yet spayed (and delivered a litter at some point in her young life) and we're getting conflicting advice from two different veterinarians regarding when it is safe to spay her. Our vet is willing to spay her 6-8 weeks post treatment, the vet that the rescue uses (and administered her heartworm treatment) suggests waiting six months before spay.

I'd like to be conservative and ensure that all of the dead worms have cleared her system before subjecting her to surgery but I also don't want her to unnecessarily go into heat either (that said, our other two dogs are spayed females and she doesn't have access to any male dogs so pregnancy isn't an issue.)

Thank you for your website, it's been immeasurably helpful!


Hello, Jodi,

The physical bulk of the dead adult heartworms should be totally dissolved by 5 to 6 weeks post treatment.

Theoretically, this means that you have no more risk than a dog who never had heartworms by the time you get to the six-week mark.

However, there may be weakened pulmonary arteries as a result of the downstream movement of dead worms and partial blockages that result. These weakened areas are more susceptible to breaking and bleeding under stress.

This accounts for dogs who get the go-ahead for return to normal activity, and have a bleed when they start exercising again. This is rare, but it does happen occasionally (like, for me, 6 times in 30 years).

This would be more a factor in exercise than in anesthesia, in my opinion.

Six months sounds like an arbitrary figure, but if the dog isn't healed by then, it probably never will be.

At six weeks, you've just gotten rid of all the chunks of worm, so you could conceivably have some need to heal.

I have spayed heartworm positive dogs because there was a strong risk of unwanted pregnancy, which would be a mess in the situation they were in. If the dog seems healthy otherwise, I am okay with this. Of course, this is in a dog that I am actually seeing and examining (which I cannot do with yours).

You make a risk versus benefit decision with anything you do.

Since you can prevent exposure to the male, I'd have a tendency to wait at least till three months post treatment. My bias, based on experience, may be nothing more than my own prejudice. There's a lot of gray area here.

Good luck.


Can heartworm lead to hair loss? Or can the preventative Interceptor cause hair loss? Since he's recently adopted, I'm not sure what's typical shedding for my dog (Chow-Corgi) for this time of year. Near his hind quarters, his hair is coming out in chunks. He is otherwise showing no clinical signs.

Janet Evans

Dear Dr,
I am the very proud mother of the best dog in the world (sorry you other mothers...) named Riley who is a Lab Mix I got from the pound 7.5 years ago. He had a rocky start, getting an auto-immune disease when he was about a year old and went on/off prednisone a handful of times over the next few years, seeming to need smaller doses for less time during each flair-up. The vet seemed very sad that first episode and appeared to strongly be preparing me for the realization that Riley would be living a short and troubled life - but my priceless companion has been auto-immune-disease-free for about 4 years now (it went away? is that possible?) Plus he has a number of "lumps-and-bumps" now that the vet says are just fat-based fluid-filled sacks that come with age and are not-pretty but also not-harmful. The lump on his side is the size of a good grapefruit.
He went to the vet 2 months ago for poor exercise tolerance and she ran a barrage of blood tests (all good) and felt it was probably arthritis, giving him some nutritional supplements. He went again last night for the gradual onset of panting in addition to the exercise intolerance and she ran tests to find he is positive for HW. He is not coughing. We are awaiting the "confirmation test" that should be back in 10 days before starting treatment. She X-rayed him and saw "a good-sized round mass in-between his heart and his lungs which could be the worms or could also be a tumor." She saw it on one view but not on the other. He tested negative for HW 8 months ago (November) so, I assume with no mosquitoes in Ohio in the winter months, got this 3-4 months ago at the most.
You are truly an angel here on Earth for answering questions and I know God will find a place for you some day... A couple of questions that I have: Is it that "confirmation" lab test that is sent out that tells me what "Stage" Riley is in? Is it a good sign that he has not yet developed a cough? Do tumors and worms look alike on an X-ray? Does his health history complicate his ability to go through the usual HW protocol you describe so thoughtfully? Do you think my best friend can do this? It will break my heart to an extent I can't describe to lose him (I might die with him) but above all else I don't want him to suffer.
Bless you for your precious time.


Hello, Lynn,

I have not seen hair loss associated with either the heartworm disease or with the oral preventives. Sometimes there is a spot of hair loss where topical preventives are applied (such as Revolution or Advantage Multi).

I would be looking elsewhere for the cause of the hair loss.



Hello, Janet,

A really enlarged pulmonary artery trunk looks almost like a growth on the side of the heart base when you look at the X-ray from the ventro-dorsal view (dog lying on back, X-rayed from the underside of the chest). This is called "pulmonary knob" by some folks.

While it is possible that your previous heartworm test was a false negative (fewer than four worms can certainly be missed on the test), I would think that at least the dog wouldn't have had much of a worm burden. Thus, it seems very unlikely to me that a dog in that condition would develop a huge pulmonary artery in such a short period of time. This makes me very concerned that there is a mass of some kind in the chest.

The confirmation test is a more sensitive test for the presence of the adult heartworm protein. Commercial laboratories give us "quality control" when we don't believe our own results. It is basically just a "yes or no" test, though.

It would not tell you anything about the dog's health, other than whether or not heartworms are present. Small numbers of heartworms generally are quite well tolerated, causing no changes in the dog's health or appearance (incredibly enough).

In other words, if a dog with one heartworm is coughing, he is coughing for some other reason.

Dogs with a history of auto-immune disease can have a relapse triggered by any major illness or event. So it is theoretically possible that going through the heartworm treatment could do that. I really don't have specific experience or expertise in that particular situation.

I am certainly not able to make specific recommendations for your dog. Your veterinarian knows your dog and has seen the tests and X-rays, and is the best person to advise you.

That being said, your description does not put heartworms very high on my list as the cause of this dog's "ain't doing right" condition.

If nothing else turns up, you might ask your veterinarian about referral to an internal medicine specialist.

Good luck.


Thanks, Doc,

Another question: can the ingredient in Interceptor cause drowsiness or vomiting in some dogs? Just gave him month number 3 dose of Interceptor a few days ago and he seemed to get really drowsy, his eyes weren't as wide and bright; just didn't seem to feel good, he vomited 9 hours later. Last month's dose was given with Benadryl, which causes drowsiness anyway, this last dose was not given with Benadryl. He did have a reaction (vomiting, increased respiratory rate) 2 1/2 hours after his first dose (in hospital). The vet said this reaction happened earlier than in most dogs. I'm wondering if he could be sensitive to the ingredient and if it would be better to switch to another product, and what is the protocol for switching products?


Hello, Lynn,

There are some specialists who prefer not to give Interceptor to dogs who already have heartworms, particularly if they have circulating microfilariae (baby heartworms).

I have had numerous dogs who became positive while taking Interceptor, and I allowed them to keep taking it with no problems.

However, if there seems to be a problem every time you give it, I would ask your veterinarian about switching to Heartgard, at least temporarily. That seems to be less of a problem for dogs that have heartworms already (at least in some cases).

It would be worth a try.

Share your concerns with your veterinarian.


Thanks again for the info. I have shared my concerns with the vet; the vet would like to keep him on the Interceptor and monitor his reactions for now because of the resistance of the Heartgard. I didn't realize that the resistance issue was specific to Heartgard. Can you explain this? Because its been around longer? Used more? Does this seem to be the case all over or specific to the southern regions?

Another vet pointed out that the dogs hair loss was of no concern; just shedding his undercoat. Difficult to know what's normal with a very recent adoptee coinciding with very recent diagnosis.

I just got the dog back two days ago from injection 1. He seems to be doing well.

Awhile back you mentioned the importance of putting pressure on the injection site to avoid infection. A vet friend in Atlanta who sees far more cases than AZ, told me to make sure that the injection site gets shaved before administering the injection. He's seen some bad secondary infections from dogs who were not shaved at the site. I just wanted to pass that along for everyone else about to go through injections now or when the immiticide becomes available to you. My dog was shaved and the injection site looks great, no swelling or redness. He's on tramadol for pain, and is only exhibiting mild soreness.


Hello, Lynn,

In my practice I have seen about the same rate of failure percentage-wise with Heartgard, Interceptor, and Revolution. I had more dogs on Interceptor, so I had more failures with Interceptor. The percentage was the same.

Carmel Hunt

Hi. I have a 12 year old mixed breed who has been on Heartguard preventative most of his life. Unfortunately, he recently tested positive for heartworms. We live in the South, and he is an outside dog. Anyway, the vet said because of his age and the expense that we should just give him prednisone, doxcycline, and sentinel, and that he would eventually suffer from congestive heart failure. Will this regimen even help? What exactly will it do? What is the pattern of treatment? The vet mentioned to give him the prednisone alternating months. What do you recommend for the frequency of these meds?

Gina Downs

Forgot to mention ... the vet had to stick him twice unsuccessfully and then changed needles and successfully administered on the third try.


Hello, Gina,







Call your veterinarian and report this situation.

Best wishes.

Gina Downs

Thank you so much.
We did call our vet and he said to give Ecotrin low dosage. We did and our cocker finally got comfortable.
This morning, he is walking fine and is almost as merry as usual.
Unfortunately, we have to have the second shot administered in another hour or so.
I want to choke the irresponsible owner who failed to give this fabulous dog heartworm preventative. In fact, ANY owner who doesn't take this disease seriously. Don't wait to see first hand how painful the 'cure' can be, you can't imagine the pathetic, helpless look your dog adopts when under this kind of stressful treatment.
GIVE THE PREVENTATIVE and GET SERIOUS about giving it according to protocol.

Thank you, doctor, for listening and giving valuable advice.


I have a 6 year old Golden Retriever mix that I adopted from a local animal shelter three years ago. They were a small, low budget operation and since he was already neutered when his previous owners surrendered him the shelter signed him over for free. He seemed very vibrant and healthy so we opted to use Southern Agriculture's walk in vaccination clinic to get his shots, but unfortunately did not get a comprehensive medical exam. The following year we scheduled Tanner for follow up shots and a full exam because his breathing had become noticeably quick and labored and he seemed to have trouble getting comfortable and would roam and switch locations several times before settling and going to sleep. He tested positive for heartworms, and his chest X-ray showed significant signs of infection. Dr. Poteet put him on Doxycycline and Heartguard, and Prednisone I think, and a few weeks later he started the Immiticide injections. Shortly after the final round of shots my husband and I went through a bankruptcy and divorced. I took Tanner with me when I relocated, and have just recently been in the financial position to start taking him to the local vet. It's been a little over a year and his recent bloodscreen tested negative for heartworms. She said everything looked good, but I am still concerned because his breathing is still fast and heavy, and he now gags and coughs, sometimes vomiting clear liquid. The only thing the vet found was a yeast/bacterial infection in his ear which has been treated and since gone away. Should I be concerned about the breathing and gagging? He just doesn't seem comfortable and I can hear him breathing from across the room. He will take several rapid breaths and then pause, wheeze as if he is straining, and then let out a heavy sigh before continuing with the same pattern. He also has excessive thirst. It's not unusual for me to fill his indoor bowl two to three times a night after I've gotten home from work. Are these symptoms normal after heartworm treatment, or are they totally unrelated? Any advice or insight would be greatly appreciated!


Hello, April,

Those are not normal findings after a heartworm treatment.

If I were seeing a dog with this description, I'd be doing a complete blood count, Biochemistry panel, and chest X-rays.

You should share your concerns with your veterinarian who is actually seeing your dog.

When they don't hear from you, they assume that things are going well.

Get in communication with your veterinarian and tell him/her that things are getting worse and that you are worried.

Good luck.


I have a 10 year old Siberian Husky who recently tested for mild/severe case of Heartworms. He's presently going through the treatment process (shots completed 15 days post now) and is feeling and eating better, but my question is regarding his leg. A couple days ago his leg grew to about double it's normal size and vet put him on furosemide for pitting edema. The vet stated that its a sign that his body is working hard to fight off the worms and it is a good and bad sign, is this true? How concerned should I be right now about his kidney failure. I understand his age is not on his side right now. We just moved to this town so trust in my vet is not at 100%. Thank you for your time!


Hello, Michael,

When heartworms die and break up, the pieces can block blood vessels. This is generally in the lungs. The inflammation involved in the process could certainly cause a blood clot to form somewhere else.

It is not common to see a leg swell after treatment.

I feel sure that your veterinarian is using a safe dose of furosemide (a diuretic, generic for Lasix), so I wouldn't be too worried about the kidneys on that account.

If the leg swelling does not go down rapidly, be sure to tell your veterinarian. Just because your dog has been treated for heartworms, this does not mean he cannot have other diseases.

Usually a big leg means a swollen lymph node that won't let fluid drain. It can also be an infection in the leg itself, or inflammation from some other cause.

Be sure to keep your veterinarian informed of your dog's progress.

Good luck.


My dog is 8-9 weeks post immiticide treatment. My vet had scheduled an 8 week check-up and I was told it was to be for a HW antigen test.

I moved to another state. Just had the dog tested at the new vet 8 weeks post immiticide treatment. The vet drew blood, came back about 10 min. later and said he was negative. Great!

Just got a call from the vet that although the test was negative, he went back and looked again afterward and he saw small traces of antigen and wants to test again and have it sent to a lab.

Can you guess how this may have happened? Can a Snap test change from negative to positive?

Is 8 weeks too soon to do a SNAP test? What is the recommended schedule for testing to see if the worms have cleared?

Should I be keeping the dog exercise restricted (no hiking with me)until he tests negative?

I don't use "blessing" very often, but your blog has been a blessing during this long ordeal.

Thank you for your time!



Hello, Lynn,

At 8 weeks post Immiticide treatment, we would not expect any physical chunks of worm to still be present. Thus, a gradual return to normal activity is what we usually recommend at this point.

Even though there are no "chunks" of worm left, there can still be heartworm protein (antigen) circulating in a dissolved form in the blood stream for four to six months after the Immiticide.(This is per Dr. Ron Blagburn, heartworm researcher at Auburn University).

We routinely test at four months post-Immiticide, but if the dog were still antigen positive at that point, I would test again two months later.

Bear in mind that the antigen test often gives false negative results if there are fewer than four adult female worms in the dog's body. It is possible to have a negative antigen test and still have a small number of worms that have escaped death in the treatment. This is unusual, but possible.

From your description of your situation, I would ask your veterinarian about delaying the follow-up test until four months post-Immiticide.


Is there anything you can give a dog post Immiticide to alliviate symptoms, more specifically the pain and coughing/gagging?


Hello, Lara,

We generally send our patients home with prednisone for the inflammation in the pulmonary arteries.

Most patients only have pain at the injection site for a couple of days, if at all (most dogs do not seem bothered, but some are very painful). We generally use tramadol for pain in these cases.

You should call your veterinarian and let them know you are having problems.

Good luck.


Hi Doc,
I have a 5 year old Rottweiler who has completed his heartworm treatment but is continuing to lose weight despite my increasing his food intake, I have already wormed him with Pancur. What else could be causing his weight loss? He was 105 before treatment now he weighs just 80.


Hello, Charles,

This is not expected with the heartworm treatment. The weight loss should be worked up as though the heartworm treatment had never happened.

If stool exams are negative (and the panacur was a good start), the next step for me would be screening bloodwork - CBC, chemistry panel, thyroid.

Nothing there, then imaging of the chest and abdomen.

I think it is very unlikely that this related to the heartworm treatment. Immiticide could be toxic to the liver, but that is a very rare event. The bloodwork would indicate liver damage.

Routine blood tests won't tell you about liver function. There are other tests for that, like bile acids. The liver assembles what you eat into a form that can be used or stored.

Weight loss is either:
1. no access to proper food
2. inability to digest food
3. inability to absorb nutrients from the gut into the bloodstream
4. inability to utilize the food (liver disease or diabetes, for instance)
5. nutrients being consumed by parasites
6. nutrients being consumed by fast-growing cancer cells
7. nutrients being lost via kidney or gut damage

You need to take this guy back to your veterinarian.

Good luck.


My 14 1/2 yo flat coat retriever rescue was cured of heartworms about 12 years ago. I am curious as to whether this condition/treatment many years ago could have resulted in some damage and is a reason for his rapid breathing, at this senior age. We realize he is old, has arthritis and likely CUshings (I.e. almost constant panting). He is now on tramadol, about 1 wk on novifit so far. Blood test did not show any unusually high readings, negative for parasites in stool. No heart or other problems during examination. Due to his age and how stressed he gets when we see the vet we are reluctant to run too many tests, and would not want to put him on the drugs for cushings. He is due for an ultrasound in a couple of wks. It is difficult to tell if this almost constant rapid breathing (about 64 breaths a minute)even when sleeping is because he is in pain. His gums have always been a light pink. His appetite is good as well as his bodily functions. He does seem to tire easily on the way back from a walk and can get wobbly. He continues monthly iverhart max. We just want him to be as comfortable as possible, and seeing him decline is heartbreaking. We have the highest confidence in our vet. Could his heart or lungs be functioning at a diminished capacity because of heartworms at an early age?


Hello, Cindy,

I think this is unlikely to be a major component of your dog's problem. If he had suffered much heart and lung damage at the time, he probably wouldn't have survived to be 14&1/2 years old.

I understand your concern about stressing him with diagnostic procedures, but they may allow for a treatment that will improve his quality of life, if not actually extending it.

Just keep sharing your concerns and observations with your veterinarian.

Good luck, and thanks for reading and writing.

A Facebook User

Thank you for this blog and the concise, well-communicated information. Would you please help clarify my dog's situation for me? She appears to be a long-haired Chihuahua, adopted from the shelter on January 12. On January 4, the shelter listed her as HW positive based on the IDEXX test. They "aged" her at about six months and she weighs about 8.5 pounds; she was spayed January 9. She came home with five days worth of doxycycline.On January 13, we took her to our vet, who did a HW panel, which also came back positive. She had two views shot on January 19, which came back completely normal, and no microfilariae were detected. Also, the vet estimated her age at 8 months rather than six months. We continued the doxycycline for three weeks, then she got her first injection of Immiticide on February 3. We were told at that point that she would need her second injection in 30 days, and no continued doxycycline. however, I see that you mention two injections in 24 hours as standard protocol. On top of all this, my father died on January 15, and I've been preoccupied with all that entails, and now I'm confused about the right treatment for Josie, not to mention the challenge of keeping a very friendly, very happy, apparently otherwise very healthy young dog quiet! Oh, and congratulations on your daughter's Peace Corps work - very impressive.


Hello, Facebook User,

Since heartworms take six months to develop to a detectable stage, we know that your dog is older than six months (though we don't know how much older).

The normal appearing chest X-rays and the very young age of the dog mean we are probably dealing with very few worms. This makes the prognosis pretty good.

Very small dogs can have problems with very small numbers of worms, simply because they don't have much room for the worms to get clogged up in. Two worms in a tiny dog take up a lot more of the pulmonary artery volume than ten worms in a huge dog.

The effect of the four weeks of doxycycline can last for up to 3 months, so that's why you aren't taking it again.

I suspect that if you simply ask your veterinarian about it, they really are planning to do two injections when you return. I suspect this is just a little glitch in communication, as it sounds as though your doctor is doing a great job for you.

Always ask your veterinarian when you have questions. We are often so sure that we are great communicators, and don't realize we have not fully succeeded in that area.

We would much rather you'd keep asking until you are satisfied that you understand the answers.

As far as keeping the dog quiet, we just try not to encourage any strenuous exercise. It is not desirable to keep the dog in a cage for two months.

The exception would be a dog who is having noticeable complications, and then we often do confine them to cage rest until those complications resolve.

Thanks for the kudos to my daughter. She is happy in her work, and that makes me feel like a parent who didn't screw up too badly.

Thanks for reading and writing. Don't forget to call your veterinarian with your questions.

karen brown

I was wondering if the worms inside the heart produce more babys. Or if the larvae only comes in through the blood stream via a misquito bite??


Hello, Karen,

Oddly enough, the answer to both of your questions is YES.

The adults in the heart do produce babies that circulate in the bloodstream (microfilariae).

These babies are like Peter Pan - they never grow up.

Babies that are sucked out of the dog by a mosquito undergo a change inside the mosquito. Then they ARE capable of growing up when the mosquito transmits them to another dog (or even back to the same dog).

I couldn't take blood from an infected dog and infect another dog, no matter how many babies were in the blood. The mosquito is not only a carrier, but an essential part of the parasite's life cycle.

Thanks for reading and writing.



I posted earlier on your site about my 6.5 lb. rescue Brussels Griffon going through heartworm treatment. I was worried she was too small to withstand treatment. I did treat her with Immiticide - 3 shot protocol and pretreated her with doxy. She did beautifully throughout the treatment and seems to feel so much better!

I took her for her 6 month follow-up yesterday and I was told she is still showing as heartworm positive. As I'm sure you can understand, I am just sick about this. Was testing 6 months after treatment too early? Should I expect to put her through treatment yet again? What would you do in a case like this? I appreciate your input. My vet is out for the week so I'm in limbo here. Thank you again.


Hello, Holly,

My concern would be about the timing of the treatment. Unfortunately, the period between infection by the mosquito and six months later is a period that we cannot detect the developing heartworms. For about four months of this period, the parasite is not susceptible to either the preventive or the Immiticide.

It sounds like there were some developing heartworms at "just the wrong stage".

Sometimes we delay treatment until six months after the mosquito season for this reason. This is also why we want to continue (or start) heartworm preventive treatment even though we have diagnosed the presence of adult heartworms. We don't want more developing.

It is also possible that the Immiticide just wasn't 100% effective. It is a sad fact that nothing is 100% effective 100% of the time.

Your veterinarian is the person best equipped to discuss whether you should be undergoing Immiticide treatment again, or just re-testing in a few months.

Thanks for reading and writing.



Our little man just had his treatment last night. We were allowed to bing him home, and have him in his crate at all time except whe we take him out to do the restroom. Our problem is he is a marker and likes to run around before he does his business. Is there any way we can get him to go potty faster so he is not getting excited? He also hasn't had a bowel movement in 24hrs which is not common.


Hello, Martha,

I would just keep him on a short leash. If you walk around for quite a while, that should not be a problem.

What we are trying to avoid is increased cardiac output and higher blood pressure.

The dog is not going to stay comatose for weeks. We just limit his activity so that he cannot do aerobic exercise. We also try to avoid sudden bursts of vigorous activity.

Getting a little excited is unavoidable, and I really wouldn't worry about it. Just don't let him run loose.

Good luck.


My 3 year old "mutt" had the 2 dose tx for HW on may 5th. He still has an unusually large lump on his back that seems to be right on his spine. We took him back to the vet and she says that although it is not "normal" he is ok. No fever and still eating and drinking ok. He has had no coughing or shortness of breath. I am just concerned because it doesn't seem to be going away. Today when I took him out his stool had a lot of mucus. Are these things I need to be concerned with and is there anything I can do?

Thank you for your time and concern


Hello, Ruthe,

A lot of mucus in the stool usually means some sort of irritation in the colon. This could be diet, eating garbage, intestinal worms, and so forth. I doubt it is related to the heartworm treatment. It would be good to take about a tablespoonful of a fresh stool (within 12 hours after it is passed) in for your veterinarian to check it.

The lump on the back sounds like it could be an unusually severe reaction to the Immiticide injection. These are rare. Usually the swelling gradually goes down. I have had one several years ago that broke open and drained.

I would ask your veterinarian if she would be willing to check the lump weekly.

Good luck. Stay in close communication with your veterinarian.


Hey Doc!

Your blog is an awesome resource! I wish I had found it before I did the HW treatment in my rescue.

I have a question about post-treatment. SD is a mix and tested high positive about a year ago when I found her. She had been positive for about 18 months before that (neglectful, undeserving former owners).

We did her treatment at the end of March and she did about as well as expected. However, she seems to still have injection-site pain. It's not constant, but sometimes when she's running around she'll cry out and tremble afterwards. I give her tramydol and in a day or so after the incident, she's usually okay. Is it from the injections? She's a 7 year old, 40 lb mix and did the 3 injection series. She had the most trouble with the pain and coughed very little.


Hello, Scotti,

This is pretty unusual. I would let the veterinarian examine to see if there is a fluid pocket or something.

Good luck.


We rescued a Boxer over two years ago just after she was treated for Heartworms. For a few months after her treatment she had a cough, however it did eventually clear up. Now two years later she is starting to cough again. She is on regular heartworm meds and is an inside dog. This is her first summer in Arizona so I was wondering if that could be the problem or if we should be worried that she has hearworms again? Can you please help?


Hello, Jennifer,

Even if the heartworm preventive has not been 100% effective, it is very unlikely that your dog would have acquired enough worms to cause illness. I highly recommend that you take her to your veterinarian to determine the cause of the cough.

Laura Richards

Hello! Thank you so much for your very informative and well written blog! I am with a pet rescue. We rescue many dogs that test positive for heartworms and I am always researching to find the latest information as well as what various vet hospitals are recommending. I hear many rescues tell how they are using the "slow kill" method for asymptomatic heartworm positive dogs. ie using a monthly preventative or ivermectin vs the traditional Immiticide, both because of costs and many state that it is easier on the dog. Do you have an opinion on this? We are still using the standard Immiticide for almost all of our heartworm positives and have been lucky in rarely seeing any adverse reaction, most dogs seem to do very well following treatment.
Most recently, we had two beagles come to the rescue. Both tested heartworm positive and both were treated with Immiticide about a month ago. After a few weeks of cage rest, we discovered that the female was pregnant, she was too early to tell when she was treated with Immiticide. There seems to be little information on the use or safety of Immiticide in pregnant dogs and we of course would have not treated her had we known she was pregnant. She is now a day or two from having pups, unfortunately, her breathing has become somewhat labored. X-rays are showing bronchitis which our main vet said is typical after a heartworm treatment. Her bloodwork is also showing high WBC, low HCT, low platelets, low calcium. We and the vet are unsure if a c-section would be easier on her or to let her have the pups. Just wondering if you have ever had experience with a similar situation?
Thank you, love your blog!


Hello, Laura,

I am happy to say that I have never had to deal with the difficult situation that you describe with this pregnant beagle. Your on-site veterinarian will be your best resource by far, here.

The "slow kill" or "soft kill" is no longer recommended by the American Heartworm Society. The problem with treatment is the dead worms shifting position and floating downstream and creating blockages and inflammation. When you treat the dog with Immiticide, you can predict when this will occur and administer anti-inflammatory doses of prednisone and restrict the dog's activity.

Even if the heartworms do die with 2 years of ivermectin (or 3 or 4, and I have rechecked positive dogs year after year), you will not be able to predict the timing. Will you restrict the dog's activity for 3 years?

The only time that I do this is when I have an elderly patient with very few worms, or the effective Immiticide treatment is not possible, due to the owner's financial circumstances.

It is below the accepted standard of care.

natasha lynn

Is post treatment injection site swelling common? Our dog finished treatments about 3 weeks ago and is doing very well. Our only concern is a somewhat hard bump where they told us her injection site was. It was larger and has gone down. She shows no signs of pain or discomfort when we touch the area. She is a shepard mix around 2 yrs old who weighs about 42 lbs. She is a rescue that had heartworms before we adopted her.


Hello, Natasha,

I would not say that swelling at the site is common, but it certainly does occur.

The fact that it has decreased in size is good, and it will probably resolve completely after a few more weeks.

I have had one patient that sloughed out a golf-ball sized area of tissue, like a terrible spider bite.

Most patients experience very minimal swelling (if any), and that usually disappears within days.

Your experience is not unique, but fortunately occurs in a small minority of patients.

If you have not done so, you should let your veterinarian know about this.

Karen Conley

We have a 12 yr old Jack Russell Terrier who tested positive for Heartworm last week. The only symptom he had was that he lost 3 lbs --no coughing and energy level is normal. Our Vet started him on Heartguard, Doxy and Prednisone. The plan for treatment is to wait 3 months then start the Immiticide injections (one injection, then 2 more 24hrs appart one month later). X-rays showed a slightly enlarged heart,but not bad. Blood & urine were both normal and he said his Liver and Kidneys are fine. In your opinion, how do older dogs usually do with the Immiticide treatment? Also, is it normal to wait 3 months to start treatment, or would sooner be more beneficial? I appreciate any advice...thank you


Hello, Karen,

The weight loss is unusual in a case like this, so one wonders if there is some other factor present that has not yet come to light, despite your veterinarian's very thorough evaluation.

The treatment that has been started sounds appropriate to me.

I usually start the first Immiticide injection after one month of doxycycline. It is possible that your veterinarian has a specific reason for waiting longer. I would recommend that you discuss this with him/her, since you have questions.

Generally speaking, the doctor seeing your pet is the one best equipped to answer your questions.


I adopted my dog a week ago. I was informed that he was HW positive, and that the shelter will cover the cost of treatments necessary. I took him to the vet yesterday, and was told that they will start treatment in 6 months. In the mean time, I am to give him 100 mg of doxycycline a day (50 mg every 12 hrs). I am unsure of how much exercise I should give himduring the 6 months before he gets his first shot of immiticide. Is this common? Should i cough up $200 and get an x-ray taken to be sure it isn't advanced. He was tested positive on Sept 2, and the vet's note says he's a good candidate for adoption. He has a lot of energy, though he does well in his crate when I'm at work all day. I'm also concerned about his sneezing and stuffy nose (thickish mucus comes out of his nose when he sneezes). But what really worries me is, every hour or so he would stop and start breathing heavily, with his hind legs stretched out. It's like he's having trouble breathing. The vet told me to record this as it happens and email it to her. Are the sneezing, mucus, and heavy breathing related to the heartworms? Any help with my baby would be greatly appreciated! Thank you!


Hello, Mary,

The mucus and sneezing are not likely to be related to the heartworms, and they may very well be related to the heavy breathing.

I would be concerned that the dog has some other respiratory problem (an infection or even a foreign body up nose).

Heartworms are more likely to cause poor endurance and coughing.

If the dog were limping and were positive for heartworms, we would be looking elsewhere for the cause of the lameness. I would be looking elsewhere for the cause of this respiratory problem.

Sneezing out snot is not normal and the dog needs to be examined. Go ahead and get your videos, too, but the doctor needs to see the dog.

Waiting six months before the heartworm treatment is often done to be sure that any immature heartworms now present will be mature enough to be killed at treatment time. Otherwise, if you treat now, you may have to treat again later.

In addition to the doxycycline treatment, the dog is usually put on preventive medicine, with Heartgard being considered the safest drug in this circumstance.

It sounds like the veterinarian is being conscientious, but she is operating on the information that she has in hand. She needs to see the dog. Don't forget the videos.

Good luck.


I adopted a dog last week from the Humane Society. The dog tested positive for HW. After contacting the clinic he was first admitted to by his previous owner, I found out he was Stage 3. The owner had given him heartworm preventative 8/27/12 and I started the injection treatment 9/20/12., two days after I adopted him.

I am doing my best to keep him calm but I feel that I am just hurting him. When I am not home he is in the crate he cries or acts like he's digging. And when arrive home, is super hyper and jumpy. Besides that he is always relatively calm.
Everything seemed to be going fine until this evening when he started tremoring then vomiting clear mucus about 6 times. ONE of the times it contained specks of blood.

He did not eat this evening and when I tried to pick him up,he yelped in pain. 2-3 hours later he is no longer tremoring and vomiting mucus.

He was on tradamol from Thursday to Saturday evening. And is on predisone every other day. He has a pill Thursday and Saturday and will have one tomorrow morning.

What is going on? Is this normal or are these severe complications?


Hello, Jessie,

Sorry about the delay, but for some reason the comment feed didn't get to my email like it's supposed to.

As you have probably already contacted your veterinarian (and if you haven't, then DO), you know by now that this is certainly not "normal".

These are not the worst complications I have seen, but usually would require more aggressive treatment. I would have recommended restricting the dog's movement (staying in the crate, or hand-walked on leash to eliminate) for several days. I would also have increased your prednisone dosage for a few days.

It is important to let your veterinarian know what is going on and follow his/her recommendations.


Thanks for getting back to me. I did contact my vet and he said though not normal that it is part of the process but if the vomiting mucus happens again to let them know. However, today he started having a cough every few hours.

My dog is currently predisone every 48hours.

Thanks for getting back to me.



I recently noticed my dog's ribs enlarging. The vet said he had Stage 3 heartworms. Could this enlargement be a sign the treatment is not working?


Hello, Nathan,

Normally the size of the rib cage can't change much. It is more likely to look different if something else is changing, like a shrunken or swollen belly, or so much weight loss that the ribs stick out.

If your dog is being treated and his outward appearance has changed significantly, then something strange is going on. That is not to be expected.

Time to get him back to you veterinarian for re-evaluation.


Hello, i adopted a wonderful dog from the spca. they told me she was 2 years old and was just recently tested positive with heart worms and that they were young and treatable with pills. i took her to 2 different vets and have paid already over $500 i can barely afford my own medication... i kept asking the vet questions about signs to look out for to know if she was about to go. he simply refused to give any sort of answer, so here i am unaware of what to look for. she has been getting worse. all he told me is that her heart and lungs are damaged from adult heart worms and that her intestines are pretty torn up as well. i do not know what to do. i do not know how badly she is suffering. because from everything i have been reading even with treatments that cost an arm and a leg, there will of course not be any way to fix her heart and lungs and intestines considering how damaged they are. she is always licking, and gagging. vomiting, hacking up foamy loogies, wheezing, breathing heavy, cant run like she used to without having to stop and cough or catch her breath. i just wish i had SOME sort of idea at least a little bit, of what to do. i can not handle having her go and me finding her or seeing it happen. i am not emotionally strong enough. ii am so torn up that the spca lied to me about her. i love her so much.


Hello, Victoria,

I can appreciate you frustration. You wanted to give a home to a dog who needed one, so you went to the shelter.

There isn't a good way to reliably determine an adult dog's age. You look at the dog's overall condition, and particularly at the wear and condition of the teeth. You compare this to the appearance of the dogs whose age you know, and you try to fit the dog in somewhere. When the SPCA gave you an age, it was probably their best guess.

The recent diagnosis may have referred to the fact that they just recently had the opportunity to test the dog.

The blood tests for heartworm don't tell us anything except "yes or no". To look at the progress of the disease, they would have had to at least do chest X-rays, which the shelters typically will not be doing as part of a checkup if the dog is acting okay.

Heartworm disease is progressive, so she might have acted pretty good at the shelter, but begun to deteriorate soon after adoption.

If her condition is deteriorating rapidly, then the long-term prognosis is not good.

While treatment to get rid of the worms will not heal the damaged heart, the lungs will get better when the worms are gone. Also, the damaged heart will have much less work to do, so the dog may be able to function pretty well when the worms are gone.

The fact that she seems to be losing ground pretty fast is the troubling thing. She may not be able to last long enough to deal with the treatment and subsequent breakup of the dead worms.

I am sorry that I do not have an easy answer for you. It sounds like your veterinarian is trying to be thorough, but that you guys are not communicating very well.

Try putting your concerns and questions in writing and leaving them with your veterinarian. Keep asking until you feel like your questions are being answered.


Our little 5yr old chihuahua/dachshund rescue pet just underwent her second injection after being diagnosed with later stage heartworms. My concern is that she has very high anxiety in specific situations. Tonight there is a thunderstorm, which means she is panting VERY heavily, and her breathing/heart rate is much increased. Her whole body shakes uncontrollably and nothing calms her. (Though she's glued to my side all along). This is normal behavior for her during a storm, but I'm concerned about the risks caused by the increased blood flow. I don't want to sedate her. Is there a very high risk for complications in these cases?! I just need to know the potential and which things I really should be worried about. Thank you for your time.


Hello, Aaron,
I can appreciate your concern in this situation.

While the dog's heart rate is certainly elevated in a situation like this, I do not think that this is increasing your risks on the same level as aerobic exercise.

I can appreciate also your reluctance to sedate the dog. There is an amino acid product (one of the building blocks of protein) called "Composure". This is not specifically sedative, but provides relief for some dogs. It didn't work for my own dog with thunderstorm anxiety, but several clients have had good results. It is inexpensive, has no side-effects, and is certainly worth a try.

We have had some success with the Thundershirt product. It's not total relief by any means, but definitely provides a measure of comfort to our dog during storms. The product is well-constructed and durable.


my dog was tested light positve for heart worms. i now have to make a decision to do slow kill or the shots. this is because the is very over weight and seven yrs. she eats half of what my other dog eats but doesnt lose wieght. she is in very good shape other wise, aleart no cough. if i didnt know her i wouldnt think she was seven. she is a very lazy dog always has been, but still playful when she decides to be active. my question is her weight and treatment together, i dont want to lose her. slow kill sounds like i could be taking her chances away though. help


Hello, Vickie,

If by "slow kill" you mean just stayingon heatworm preventive for years, I have lost faith in that process, and the American Heartworm Society no longer endorses it.

In the case of a geriatric patient, or one that might have trouble withstanding treatment for other reasons, it is reasonable to stay on preventive and "hold the line".

Has your dog's thyroid level been checked? This is a simple blood test. That behavior is classic for low thyroid - poor activity and overweight, despite low food intake.

Thyroid hormone governs the rate of metabolism. It's really cool to see a hypothyroid dog wake up and come back to life on their hormone replacement (which is not expensive).

Thanks for reading and writing.

Linda  Duke

Hello Dr.
we recently started a HW treatment rom a vet for a dog we adopted. She was in stage 3 HW condition. We did two immicticide injections a day apart and then 30 days later 2 more a day apart. About 3 weeks ago she started to show really bad skin lesions that bleed, crust up and then bleed again. they are on her neck head, stomach and back. lots of very small ones but the 2 on her back are about2" now and the one goes almost around the backside of her neck. The vet keeps telling us this is her bodys way of expelling the worms but I havent been able to find anything online to that fact. We've had her on an antibiotic and on predisone and antiseptic baths and no improvement. Have you ever heard of this.


Hello, Linda,

Since I have not seen your dog, I cannot really advise you on specifics here.

This is certainly not an expected event following heartworm treatment.

The only thing that I can think of is that it is either something completely unrelated, or that the dying worms have gotten the body's defense system stirred up and you are having some sort of auto-immune skin disease (the body attacking itself).

If the dog is not responding to treatments as expected, then it may be necessary to get a skin biopsy to determine what is causing the problem.

Be sure to let your veterinarian know how your dog is responding (or not responding) to treatment. Sometimes we don't see something for a few days, and the telephone call doesn't really give us the true picture.


We have a "young" boxer mix rescue who is five weeks past his final immiticide injection. He has one more week of prednisone every other day. He only had one slight complication where coughing occured and the vet increased his predisone for a 3 day period and an additional 2 wks of Doxy. This was about 10 days post final shot. The vet took x-rays at that time and saw some irritation in the lungs and his heart was a bit enlarged. My question is at what point should ask the vet to repeat those x-rays? I would like to know if the "damage" is healing and the heart has returned to a normal size. I was thinking I would ask at his hw re-test. Thank you for your helpful information.


Hello, Sherri,
Sounds like this is about 3 weeks after the previous X-ray.

We usually recommend restricted activity for 5 to 6 weeks after the last Immiticide injection. At this point the worms should be pretty well dissolved, that is no big chunks left (though there may still be circulating heartworm protein that will still give a positive blood test).

I have had a very small number of dogs who seemed fine at this point, but had some damage that didn't show until the dog was stressed by returning to exercise. These dogs may cough quite a bit, or even cough up blood. They don't usually have severe problems at this point.

I think it's a good idea to talk to your veterinarian about repeating the X-ray when you go back. He/she will also be listening to the dog's chest to evaluate the heart and lungs.

You will want the return to activity to be gradual and supervised. Talk with your veterinarian about his/her recommendations.

meg yarmel

Hi Dr.

Interested in adopting 6 yr old dog(s) with former HR and cure. What tests would you recommend to determine their present health status? Would it be cost prohibitive? Can one expect heart and lung problems down the road that would require testing and tx?


Hello, Meg,

I would start with a good physical exam and current heartworm test.

A chest X-ray would be the most informative as to whether there has been damage "along the way".

I don't think that this would be cost prohibitive.

If that all looks good, then I would not expect unusual problems in the future.


Just wanted to comment because I am into rescue and fostering and have dealt with many cases of dogs coming to me with heartworms in south Louisiana (I actually have a yellow lab rescue foster that just got his second treatment shot today)...if possible of course it is ideal to find out a dogs heartworm status before adopting but I would hate to see all of the dogs down here in shelters that test heartworm positive get overlooked and put down (and down here unfortunately they get put down very quickly if no one steps up due to the immense overpopulation). As the dr mentioned there are pros and cons to undergoing the expensive and intense heartworm treatment versus just keeping them on monthly preventative and allowing the current ones to die in time. I have been through both methods with rescues and have always had vets only recommend the latter option if it is not an advanced case (and very often it is not advanced especially in young dogs). Anyway I guess my point is that the option of just continuing preventative in a heartworm positive dog- while maybe not always the most ideal- is cheap and in my opinion better than letting a dog be put down in the shelter because you cant afford the thousand for the fast treatment. So don't necessarily pass up on a good dog just because of heartworms everyone!
Thanks for this blog it is very informative!
PS I have also been hearing more and more about cases of dogs that are on monthly preventive contracting heartworms as you mentioned. It seems to be becoming somewhat of a problem in Louisiana. Yikes!


Hello, Bethany,

Thanks for taking the time to make your thoughtful post here.

While we have been having fewer problems in our area with the "lack of efficacy", when I talk to people south of us, the problem hasn't gone away for them.

debbie bullard

I have a rescue that was treated for heartworm and her hacking was only procucing a small about of phlegm and today she has a little bit of blood in it.
She is due back on the 11th of this month.
Should she be seen as soon as possible?


Hello, Debbie,

With blood being present, I would not wait until the 11th. Do call your veterinarian and inform them. If she were my patient I would want to see her as soon as I could.



I wrote to you some time back about my 6 lb Brussels Griffon rescue with heart worms. We treated her and she failed treatment. She subsequently suffered a PE and was hospitalized. We put her on Plavix and were waiting for to stabilize before retreating. She then suffered a stroke but thankfully recovered. Then she had a second one a week after the first! She finally tested negative for heart worms after the first stroke but we are puzzled as to why she is still throwing clots despite being negative and on Plavix. Could this still be an inflammatory response to the heart worms despite now being negative? We are testing for Cushing's despite the fact that she has no other symptoms. Thank you for your help!


Hello Doc~First I just want to say I have been reading your blog for the past couple of hours, while my new foster Fiona sleeps on my arm on the floor. Thank you so very much for all the invaluable HW information. I love my vet but I am one of those pet mommies that ask a million questions so to have you to run this by is great! OK, so miss Fiona (Florida native) had her 2 injections Monday and Tuesday. Was doing pretty well until this morning. Her lethargy is greatly increased. No coughing, normal amount of panting, and sleeping comfortably (except for her snoring). Her eating and drinking is very much off today, tail is just hanging and when I walk her around my yard she doesn't even put her nose to the ground. She pooped normally but doesn't squat to pee. The vet has her on doxy now (she had it for URI in Florida but had finished it before coming up to NJ) but not for the entire month prior to treatment. He didn't give me prednisone, but did say to give half a buffered aspirin once a day (she is 55 lbs) Would she be more comfortable taking something stronger? Seems half an aspirin at her weight would not do a lot to ease any inflammation. Also, is increased lethargy a few days after treatment to be expected? I know not every dog has the same effects, but don't want to run her back to the vet if it's to be expected. Thanks so much for all your help :)


Hello, Allison,

Buffered aspirin doesn't really protect the stomach. The stomach acid is much more powerful than the acidity of the aspirin.

Aspirin causes two problems. With chronic administration, it inhibits platelet function, which makes you a free bleeder. That doesn't happen with occasional use.

It is anti-secretory, so when it hits the stomach lining, it interrupts the production of the protective mucus that coats the stomach lining. This allows the stomach acid to damage the lining. I am told that we lose 1/4 tsp to one teaspoon of blood for every regular strength aspirin we take.

This is why enteric coated aspirin (like Ecotrin) is used by heart patients who take one every day. This inhibits platelet function, reducing the risk of clots, and it doesn't dissolve until it gets past the stomach.

Cutting one in half would remove the coating, so people often use the lower strength tablet and take as many as needed (like one to two 81mg "baby aspirin" strength).

There was a period of time about 30 years ago when the American Heartworm Society was recommending daily aspirin during the post treatment period, but this was later shown to be unhelpful, and the recommendation was changed.

I am not in a position to prescribe for your dog. I personally have had much better luck with corticosteroids like prednisone following Immiticide therapy.

If you are in New Jersey, it is likely that your veterinarian doesn't see a lot of heartworm disease, compared to an endemic area like the Gulf coast or the Mississippi valley.

This doesn't mean that he has no idea how to treat it. It does mean that he needs feedback from you on how the dog is doing. Since the dog appears to be having complications from the movement of the worms, he needs to know that.

With new information, he may give you a new recommendation. If he doesn't hear from you, he will assume that all is well. All is not well.


Hi again Doc. I had spoken to my vet before I posted my first question and he didn't seem overly concerned, but when Fiona had trouble standing a few hours later I called again and the vet had me come and get a few Deramaxx and says give half a pill once a day. Assume this is treating pain only, seems they think her lethargy is due to pain from the injections. They did take a while listening to my concerns so I feel they are well informed of how she is doing. Should I request a steroid also? Thanks again.


Hello, Allison,

You cannot combine these drugs. It is important that you don't add different NSAIDs together.

Deramaxx is anti-inflammatory as well as a pain reliever. It is really effective for musculo-skeletal pain and inflammation. If your problem is indeed soreness at the injection site, this should really help. My experience with injection site pain is that it usually subsides within 3 days after the injection.

If the problem is inflammation in the pulmonary arteries, then the Deramaxx may not work as well as the steroids.

You cannot combine the Deramaxx with steroids. The two together can cause serious stomach bleeds.

Keep your veterinarian posted as to how the dog is doing.


OK Doc, she perked up with the Deramaxx. Went outside with raised tail to potty and ate most of her dinner. Still moving slower but a definite improvement from earlier today. Didn't mean to misspeak, I do know to never mix the 2 drugs I mentioned. I should have said steroids INSTEAD of the nsaid. Thanks for the prompt responses, very much appreciated. I will absolutely keep my vet informed :)


Firstly, thank you for taking the time to do this blog, like others i found this late at night while trying to figure out how to help my distressed dog. We have a rescue yorkie who had his first treatment about 10 days ago. I did not crate him due to him getting overly upset when I put him in and took him out, I figured it was less stress on him to simply keep him out in a confined area with my older dog. Tonight he has been wretching and doing a deep cough maybe 6 times or so. I've managed to keep him close and relatively still. And intend to take him back to the vet tomorrow, as something definitely seems to have shifted. My vet did recommend Benadryl to help slow him down and to help with him biting on hs feet (we think it an allergy that just started). Hes been taking about 6mg the last few days and it seems to have helped with the biting. My question is can prednisone be used with Benadryl I'm hoping he will be prescribed this again tomorrow to help with his breathing.



Sorry I didn't see this until late this evening.

I'm sure that your veterinarian has told you already that prednisone and benadryl or okay together.

I hope things are going okay. Very small dogs can have more severe problems with the breakup of the dead worms. It's just the fact that there isn't as much room for the worms in a small dog's arteries.


I just would like to start off by saying thank you for sharing your wealth of knowledge with concerned readers like myself. My 7 year old adopted golden retriever was just diagnosed with heartworm last month. He was given his first shot of immiticide 6 days ago and given the second 24 hours later. He stayed overnight between injections. Upon returning home with him he seemed very restless and was panting heavily. I called the vet and was told to bring him back. She examined him and decided that it was probably just pain so she kept him overnight again to observe him and gave him a painkiller, I picked him up the following morning as he was doing better. He seemed a-ok for the next few days. I have not been crating him because he is not very active in the house just the occasional walk from room to room and when we go out we go potty and come right back in. This morning when I woke up I noticed two small puddles of was appeared to be foamy white phlegm with a yellow twinge to it no blood. I did not hear him cough it up. So back to the vet we went. She listened to his lungs and his heart and she said that everything sounded really good. She told me that she would like to hear from me if we notice any coughing, heavy breathing or abdominal breathing. So far I have seen none of these symptoms. I asked her how severe his infestation was and she wasn't sure because the main vet there did his workup and she had not seen his x-rays or test results but she figures that it wasn't terrible because they aren't spacing out the treatments more and he wasn't displaying any symptoms. That makes me feel better. Sorry to ramble on, I just wanted to give you some information about what was going on. My question is how likely is it that we will see complications like coughing and heavy breathing since now is about the time the worms are starting to die and shift and during what time frame do they usually occur in your experience? Have you seen any cases were dogs completed the treatments without having any of these problems? I want to add that he is receiving prednisone and antibiotics. I was also wondering during this style of "fast kill" treatment how soon do the worms begin to die? Do they die all at once or do they die a few at a time? Is it also common for a dog not to feel very well during this time? He seems a little out of sorts and not his usual chipper self today. But he perked right up during his field trip to the vet today ;) But he is eating and drinking and has been chewing his rawhide. Again thank you for answering questions for your readers. I have a great vet and I will definitely continue to be in touch with them, I was just looking for your input.


Hello, Karlie,

The worms usually start dying 4 or 5 days after treatment. I doubt they all die exactly simultaneously, but they pretty much all die within the same 24 to 48 hour period. Again, this is when we usually see signs of difficulty, such as those you describe.

Your veterinarian has already prescribed what sounds like appropriate medication to me. Keeping activity to a minimum is important while the dog is showing these signs of distress.

It is not uncommon for dogs to display the bad signs you have described, but most will come through the treatment okay. Keep the activity restricted, and keep in close touch with your veterinarian.

Lara R

Hi there
My question is once the heartworms break up and go to the lungs how long does it take for them to break down?
We had our 14 lb rat terrier/jackrussell treated 2 weeks ago. She started coughing/gagging Friday and the vet put her on prednisone 5 mg twice a day. By Sunday am she had laboured breathing, shaking when she breathes sometimes. The vet said there was not much to do but keep her quiet and keep on the prednisone.
She is eating and drinking, is resting a lot on her own, gums are pink and good capillary return. Not restless and does appear somewhat interested in what is going on around her.
I guess I just wonder how long before they disolve and she is feeling better. (I actually think it bothers me more than her, while she is not herself, she doesn't apper to be in any distress)
Thank you so much!


We generally consider that it will take 5 to 6 weeks after treatment before we are pretty sure there are no solid chunks of worm left. There will still be heartworm protein circulating in the blood at this point (so test is still positive), but nothing that should clog up a vessel.

On rare occasions, a vessel damaged by the process will break when the dog returns to exercise. Return to exercise should be gradual, and monitored by you.

Lara R

Thank you. We took our dog back to the vets tuesday and her chest xray had changed, there is inflammation in her lungs. She got a shot of lasix, dexamethasone and some oxygen. The vet prescribed doxy as her lymph nodes in her neck were swollen. She remained with rapid shallow brathing and couldn't seem to get comfortable friday, so the vet checked her again, no temp and he felt her lungs were much clearer (no wheeze or crackles), all signs pointed to no oxygen deprivation and despite wanting to stand all the time she looked brighter.
Today, Saturday she is the same. Rapid breathing and unable to get comfortable to lay down. The Vet said it would be at least a week before we would see a change, do you think it will be longer? Because it takes 5-6 weeks before there are no solid chunks? Or do you think we will see her slowly get better as time passes?
I really appreciate this blog, it was very helpful as was your response. That is why I came back!


Hello, Lara,

I really cannot give you any specific advice here. Your veterinarian who is actually seeing your dog is your best source of information at this point.

It is troubling that she still is having this much difficulty breathing (not wanting to lie down, but standing to make it easier to breathe).

I would hope that you will see rapid improvement over the next couple of days. If you do not, please let your veterinarian know what is happening.

Sonya F.

Thanks for all of the helpful information on this blog. Can you advise on panting and shivering/shaking in my dog that received her 1st and 2nd shots last week? Today would be 8 days past the first shot. The past 3 nights she has gotten us up at all hours of the night with heavy panting and the urge to potty. During the day, she seems completely normal. The vet has her on 100mg of Minocycline (seems to cause her nausea @ 3 tablets by mouth 2x daily) Metoclopramide 10 mg 3x daily as needed for vomiting and Prednisone 20mg. My baby is a 62# Pit Mix about 6yoa in Stage 1 asymptomatic. Just want to see if the occasional panting and shivering is normal and what it could be a symptom of. Thank you in advance!


Hello, Sonya,


I would not say that the panting and shivering is normal, nor expected.

If it has not yet resolved, you might talk to your veterinarian about backing off one or another of the medications to see if it is a side effect.

The prednisone is making her produce a more dilute urine, so she has to get up to potty more often, and drink more water to compensate for the loss.

Some dogs do have mood alteration with the prednisone, though it is usually to the good. Sometimes it makes them wacky, though. If you haven't yet discussed this with your veterinarian, please do.


I just wanted to leave a note thanking you for the wonderful advice you've given in your post and in the comments. I adopted a malamute who was heartworm positive and we just did the first melarsomine injection this morning. I've been stressing for weeks about how it was even possible to keep him confined to a crate for over two months (he HATES being in a crate) and maintain both of our sanities, but your advice regarding leash walks and aerobic exercise makes perfect sense. I live in Montana and the vets here have almost no experience treating heartworm, so my vet and I are learning as we go (the dog came from South Carolina).


Hi, Mike,

Thanks for your kind words. I hope things go well for you.

Leslie Nance

I rescued a boxer a month ago and he is HW+. He is on the waiting list for the "fast kill" method that the Rescue will pay for. In the meantime my Vet has him on Sentinel monthly. He sleeps ALL THE TIME. He is so lazy and he is only 2. Do you think this is due to the heartworms?


Hello, Leslie,

I am presuming that your doctor has already checked the dog for other medical problems.

The only way to get an idea of how much heart damage is present is to take chest X-rays.

If the dog just seems unwell, then doing some blood testing for other problems would be in order. I'd start with a complete blood count, blood chemistry exam, and a thyroid level.

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