Updated August 21, 2026

Tetralogy of Fallot (TOF) is a combination of four congenital (present at birth) heart defects that affect babies. The defects occur at the same time and change the way blood flows through the heart and lungs. TOF occurs in about 1 out of every 2,518 babies born in the U.S. each year.

Pediatric cardiologist Rukmalee Vithana of the Blalock-Taussig-Thomas Pediatric and Congenital Heart Center explains what you should know about TOF.

What is tetralogy of Fallot?

Tetralogy of Fallot occurs when four heart defects are present at the same time at birth. When TOF occurs, babies have trouble getting enough blood to their lungs, which results in the rest of the body not getting enough oxygen.

The four heart defects of tetralogy of Fallot include:

• Pulmonary stenosis: A narrowed or stiffened pulmonary valve means the pulmonary artery has trouble sending enough blood from the heart to the lungs. In some children with more severe forms of TOF, the pulmonary valve may be plate-like, with the leaflets not opening or sealed close; this is known as pulmonary atresia. The arteries that lead blood to the lungs can be very small and abnormal, making surgical correction more complicated.
• Ventricular septal defect (VSD): VSD is a hole between the two lower chambers (ventricles) of the heart. The hole allows oxygen-rich blood and oxygen-poor blood to mix, so the body does not receive enough oxygen-rich blood.
• Overriding aorta: The aorta, which is the artery that carries oxygen-rich blood to the body, is out of place and rises above both ventricles. As a result, the body gets too much oxygen-poor blood.
• Hypertrophy (enlargement) of the right ventricle: The right lower chamber of the heart is bigger or thicker than normal, making it harder for blood to go through the pulmonary valve.

What causes tetralogy of Fallot?

Although it's known that TOF occurs when a baby’s heart does not form correctly in the womb, experts are not sure what causes the defects to form. TOF could be the result of changes to genes or chromosomes.

Possible risk factors may include:

• Genetic syndromes, such as Down syndrome or DiGeorge syndrome
• Environmental factors, such as smoking or taking certain medications during pregnancy
• Family history
• Having certain medical conditions during pregnancy, such as diabetes or rubella

What are the symptoms of tetralogy of Fallot?

The most common symptom of TOF is cyanosis. Cyanosis is when the skin, lips and nail beds are blueish in color. It is the result of too little oxygen being carried through the body.

Cyanosis may come in sudden spells, called tet spells, when a baby is crying or feeding. It happens when a baby’s blood oxygen level drops quickly. During the spell, babies may have a hard time breathing. In the most extreme circumstances, they may go limp or lose consciousness.

Other symptoms of tetralogy of Fallot at birth may include:

• Difficult or rapid breathing
• Fatigue
• Fussiness
• Heart murmur
• Trouble feeding or gaining weight

How is tetralogy of Fallot diagnosed?

Some babies are diagnosed with tetralogy of Fallot before birth. The heart conditions may be seen on prenatal ultrasounds, while the baby is still in the womb.

After birth, tests for TOF may include:

• Cardiac catheterization
• Chest X-ray
• Echocardiogram
• Electrocardiogram
• Coronary Computed Tomography Angiography
• MRI

What are the treatment options for tetralogy of Fallot?

All children with tetralogy of Fallot need surgery. Most children have surgery when they’re about 6 months old. Your doctor will determine which surgery is most appropriate.

Temporary Procedures

Before the complete repair, some children may need an earlier procedure if the narrowing of the pulmonary valve or pulmonary stenosis is severe and significantly limits blood flow to the lungs. This may be performed by one of two options:

• Blalock-Taussig-Thomas shunt. A surgery performed by placing a small tube (shunt) from an artery attached to the aorta to the pulmonary artery. This shunt provides a new blood flow path to the lungs.
• Patent ductus arteriosus stent. A surgery where a tube (stent) is inserted into narrowed blood vessels and widened to keep the vessels open. In this case, it is inserted into a ductus arteriosus (small vessel near the heart) through a minimally invasive procedure in a cardiac catheterization laboratory. 

Both these options are not permanent solutions; babies will still need a full repair surgery later.

Full Repair Surgery

A full tetralogy of Fallot repair surgery involves:

• Placing a patch over the ventricular septal defect
• Removing thickened tissue from the right ventricle
• Widening the pulmonary valve
• Enlarging the pulmonary arteries if they are small 

Tetralogy of Fallot Complications

Potential complications of TOF include:

• Abnormal heart rhythm (arrhythmia)
• Blood clots
• Heart failure
• Infection in the lining of the heart and heart valves (bacterial endocarditis)
• Leakage (regurgitation) from the repaired pulmonary valve
• Death

Living with Tetralogy of Fallot

Most children go on to lead active, healthy lives after TOF treatment. They will need ongoing care and monitoring from a pediatric cardiologist. 

People who had TOF repair surgery as children may need continuing TOF treatment into adulthood, such as a second surgery or cardiac catheterization to replace their pulmonary valve. 

Heart rhythm abnormalities (arrhythmias) can occur throughout life and require ongoing monitoring. Patients should be followed by a pediatric cardiologist during childhood and continue lifelong care with an adult congenital heart disease specialist.

Medically reviewed by Rukmalee Erandika Vithana, M.D.