Bradycardia is a slower than normal heart rate. The heart usually beats between 60 and 100 times a minute in an adult at rest. If you have bradycardia, your heart beats fewer than 60 times minute.

What is it?




When a slow heart rate is normal
A resting heart rate slower than 60 beats a minute may be normal for some people, particularly for healthy, young adults and trained athletes. In these cases, bradycardia isn't considered a health problem.



  • Degeneration of heart tissue related to aging
  • Damage to heart tissues from heart disease or heart attack
  • High blood pressure (hypertension)
  • Heart disorder present at birth (congenital heart defect)
  • Infection of heart tissue (myocarditis)
  • A complication of heart surgery
  • Underactive thyroid gland (hypothyroidism)
  • Obstructive sleep apnea, the repeated disruption of breathing during sleep
  • Inflammatory disease, such as rheumatic fever or lupus
  • Hemochromatosis, the buildup of iron in organs

Electrical circuitry of the heart

  • Your heart is made up of four chambers — two upper chambers (atria) and two lower chambers (ventricles). The rhythm of your heart is normally controlled by a natural pacemaker — the sinus node — located in the right atrium. The sinus node produces electrical impulses that initiate each heartbeat.
  • From the sinus node, electrical impulses travel across the atria, causing the atria to contract and pump blood into the ventricles. The electrical impulses then arrive at a cluster of cells called the atrioventricular node (AV node).
  • Bradycardia occurs when electrical signals slow down or are blocked.

Sinus node dysfunction


  • Discharges electrical impulses at a slower than normal rate
  • Pauses, or fails to discharge at a regular rate
  • In some people the sinus node dysfunction may result in alternating slow and fast heart rates (bradycardia-tachycardia syndrome).

Heart block (atrioventricular block)

Bradycardia also may occur because electrical signals transmitted through the atria aren't transmitted to the ventricles (heart block, or atrioventricular block). The disruption of the electrical signal may occur in the AV node, the bundle of His, or somewhere along the left and right branches that transmit electrical signals to the ventricles. Heart blocks are classified based on the degree to which signals from the atria reach your heart's main pumping chambers (ventricles).

  • Third-degree (complete) heart block. In third-degree heart block, none of the electrical impulses from the atria reaches the ventricles. When this happens, the bundle of His or other tissues of the ventricles function as a substitute pacemaker for the ventricles. These substitutes result in slow and sometimes unreliable electrical impulses to control the beat of the ventricles.
  • Bundle branch block. The interruption of an electrical signal somewhere in the right or left bundle branches — near the end of the pathway for electrical impulses — is called a bundle branch block. The seriousness of bundle branch block depends on whether both branches are affected, the presence of other types of heart block and the degree of damage to heart tissue. 


Complications of untreated bradycardia vary depending on how slow the heart rate is, where the electrical conduction problem occurs and what kind of damage may be present in heart tissue. If bradycardia is significant enough to cause symptoms, possible complications of the slow heart rate may include:

  • Frequent fainting spells
  • Sudden cardiac arrest or sudden death

Risk factors


A key risk factor for bradycardia is age. The degeneration of tissue associated with many cases of bradycardia is more common in older adults.

Risk factors related to heart disease

Bradycardia is often associated with damage to heart tissue from some type of heart disease. Therefore, factors that increase your risk of heart disease may also increase the risk of bradycardia. Lifestyle changes or medical treatment may decrease the risk of heart disease associated with the following factors:



Electrocardiogram (ECG)

An electrocardiogram — also called an ECG or EKG — is a primary tool for evaluating bradycardia. An ECG uses small sensors (electrodes) attached to your chest and arms to record electrical signals as they travel through your heart. Your doctor can look for patterns among these signals to determine what kind of bradycardia you have.




  • Tilt table test. This tests helps your doctor better understand how your bradycardia contributes to fainting spells. You lie flat on a special table, and then the table is tilted as if you were standing up. Changes in the position may induce a fainting spell and enable your doctor to establish a correlation between your heart rate and fainting episodes.

Laboratory and other tests

Your doctor will order blood tests to screen for underlying conditions that may be contributing to bradycardia, such as an infection, hypothyroidism or an electrolyte imbalance. If sleep apnea is suspected of contributing to bradycardia, you may undergo tests to monitor your sleep.

Treatments and drugs

Treatment for bradycardia depends on the type of electrical conduction problem, the severity of symptoms, and the cause of your slow heart rate.

Treating underlying disorders


Change in medications

A number of medications, including some to treat other heart conditions, can cause bradycardia. Your doctor will check what medications you're taking and may recommend alternative treatments. Changing drugs or lowering dosages may correct problems with a slow heart rate. When alternative treatments are not possible and symptoms require treatment, a pacemaker is necessary.


A pacemaker is a battery-operated device about the size of a cell phone that's implanted under your collarbone. Wires from the device are threaded through veins and into your heart. Electrodes at the end of the wires are attached to heart tissues. The pacemaker monitors your heart rate and generates electrical impulses as necessary to maintain an appropriate rate.




Prevent heart disease


  • If you drink, do so in moderation. If you consume alcohol, drink in moderation. For some conditions it is recommended that you completely avoid alcohol. Ask your doctor for advice specific to your condition. If you can't control your alcohol consumption, talk to your doctor about a program to quit drinking and manage other behaviors related to alcohol abuse.

Monitor and treat existing heart disease

