Tetralogy of Fallot





If your child’s been diagnosed with tetralogy of Fallot (or “TOF,” for short), we’re here to ease your concerns, answer your questions, and give your child the best possible chance for a healthy future.

What Is It?
Tetralogy of Fallot is a combination of four related heart defects:
  1. ventricular septal defect (or “VSD,” a hole between the lower chambers of the heart)
  2. pulmonary stenosis (a narrowing of the pulmonary valve which obstructs flow from the heart to the lungs)
  3. an overriding aorta (an aorta that can receive blood from both the left and right ventricles, instead of draining just the left)
  4. right ventricular hypertrophy (a thickened right ventricle)

The main problem in tetralogy of Fallot is the VSD which is what is called a “malaligned” VSD because the septum (the muscular part of the heart that separates the left and right chambers) isn’t lined up properly. Instead, part of the septum is shifted toward the right side, which blocks the blood flow leaving the heart to go to the lungs (this is called “pulmonary stenosis”). This part of the septum also shifts the aorta (the main blood vessel carrying oxygen rich-blood to the body) from its usual position and the aorta can then get blood from both the left ventricle (oxygen-rich blood) and from the right ventricle (oxygen-poor blood).

Because the right ventricle, which is supposed to pump against the lower blood pressure in the lungs is, instead, pumping blood out the aorta to the body (which has a higher blood pressure), the muscle gets bigger, resulting in the fourth component of tetralogy of Fallot: the right ventricular hypertrophy.

Tetralogy of Fallot Causes Decreased Blood Flow to the Lungs

Normally, the oxygen-poor blood in the heart flows from the right ventricle through the pulmonary artery, to the lungs to receive oxygen and then return to the left ventricle to be pumped back out to the body. The pulmonary valve connects the right ventricle to the main pulmonary artery. In children with tetralogy of Fallot, the path of blood from the right ventricle to the pulmonary artery is narrowed (“pulmonary stenosis”). This narrowing may happen:

  • at the pulmonary valve (this is called “valvar” obstruction)
  • above the valve (this is called “supravalvar” obstruction)
  • below the valve within the right ventricle, in an area called the “right ventricular outflow tract” (this is called “subvalvar obstruction,” or “right ventricular outflow tract obstruction”)

Because the pathway for blood to leave the heart toward the lungs is blocked, some of that oxygen-poor (“blue”) blood can flow out to the body, so children with tetralogy of Fallot defect often appear bluish (this is called “cyanosis”).

The degree or amount of pulmonary stenosis in tetralogy of Fallot varies between children — and this changes the amount of “blue” blood going out to the body. Some children with mild narrowing may not be bluish at all, while at the other extreme, the right ventricular outflow tract is completely blocked off. This is called “tetralogy of Fallot with pulmonary atresia” (“atresia” is the term for a valve that’s so small that it has no opening at all).

Hypercyanotic or “Tet” Spells

Children with tetralogy of Fallot are at risk of having “hypercyanotic spells” or "Tet spells." These happen when the muscle of the right ventricular outflow tract spasms or tightens. Along with a sudden increase in the resistance to flow through the lungs from tightening of the small blood vessels in the lungs, this leads to a sudden decrease in the amount of blood going to the lungs.

More oxygen-poor “blue” blood flows out the aorta and the child’s oxygen levels (or “oxygen saturation”) decrease rapidly (this is called “hypoxia”). The hypoxia causes more tightening of the blood vessels in the lungs and a downward spiral can begin. Older children learn to squat in order to prevent or treat a spell. Although the exact mechanism isn’t clear, squatting increases resistance to blood going out the aorta and forces more blood to go through the lungs — this increases the oxygen levels and ends the spell.

How Does the Heart Normally Work?

Learn More About Normal Cardiac Anatomy »


How & When Is It Diagnosed?

Some children with tetralogy of Fallot are diagnosed before birth during pregnancy using a fetal echocardiogram (or “fetal echo”). Others may be diagnosed after birth, either because measurement of the oxygen levels in the blood (“oxygen saturation”) show that there’s “blue” blood going out to the body, or because one the baby’s caregivers hears a heart murmur.

Occasionally, children with tetralogy of Fallot have very little obstruction to blood leaving the right ventricle. In this case, instead of “blue” blood flowing out the aorta to the body, oxygen-rich blood from the left ventricle flows out the lungs (as in a more usual ventricular septal defect). These children aren’t cyanotic (bluish) and may develop heart failure symptoms just like a child with only a VSD. These children are sometimes described as “pink tetralogy of Fallot.

The diagnosis is usually made using an echocardiogram (“echo”), which also allows the caregiver to identify the specific type of tetralogy of Fallot. An echo is a completely safe and painless test that uses ultrasound (sound waves) to build a series of pictures of the heart. Most children with the simpler versions of tetralogy of Fallot won’t need a cardiac catheterization, CT scan or MRI. But some children with more complex versions may need these additional tests before treatment.

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How & When Is It Treated?

Unlike many congenital heart defects in which all or most babies with a particular defect will behave similarly in terms of developing symptoms and needing treatment, the timing and exact type of treatment for tetralogy of Fallot varies a lot from child to child. But all children will need open-heart surgery.

A “complete repair” includes closing the VSD with a patch and enlarging the pulmonary valve, pulmonary artery and the area below the valve in the heart muscle to allow blood to flow to the lungs. Enlarging the right ventricular outflow tract (the region from the right ventricular muscle to the pulmonary artery which allows blood to flow to the lungs) often requires an incision across the pulmonary valve and placement of a patch to widen the outflow tract (called a “transannular patch”). A complete repair causes the blood to follow the normal pathway through the heart.

The exact timing of surgery remains controversial, but most agree that children having hypercyanotic spells (“Tet spells”) or with severe cyanosis (low levels of oxygen in the blood) need surgery. In nearly all children, surgery will happen between 1 month and 1 year of age.

When surgical intervention is necessary in a child who isn’t a good candidate for complete repair (e.g., a very small baby, or one with tiny pulmonary arteries or other heart defects), a temporary procedure called a “palliative” procedure may be performed. A palliative procedure consists of placing a tube of synthetic material (a “shunt”) from the aorta to the pulmonary artery to increase blood flow to the lungs. There are a variety of methods of doing this. The most commonly performed shunt today is called the “modified Blalock-Taussig shunt,” in which a tube of the synthetic material Gore-Tex is placed between the subclavian artery and the pulmonary artery.

Learn More About Heart Surgery »

How Will It Affect My Child Long Term?

Children with tetralogy of Fallot do well in the long term, although many will require additional procedures later in life. In children with TOF, the pulmonary valve is abnormal and usually doesn’t function properly after the repair. Children can tolerate a leaking pulmonary valve for many years, but many will eventually require a procedure to repair or replace the valve. This may happen in childhood, but may not be necessary until children are in their 20s or even later.

In order to determine when (or if) your child will need additional procedures, we recommend close follow-up with your child’s pediatric cardiologist, including echocardiograms and MRIs to keep an eye on the function of the heart as your child grows.


Learn More About Congenital Heart Defects »

Heart Murmurs


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Read About Other Children With Tetralogy of Fallot (TOF)

Meet some of our Nemours Cardiac Center patients who know what it’s like to have TOF: