Tetralogy of Fallot (teh-TRAL-uh-jee of fuh-LOW) is a rare heart condition that is present at birth. That means it's a congenital heart defect. A baby born with the condition has four different heart problems.

These heart problems affect the structure of the heart. The condition causes altered blood flow through the heart and to the rest of the body. Babies with tetralogy of Fallot often have blue or gray skin color due to low oxygen levels.

Tetralogy of Fallot is usually diagnosed during pregnancy or soon after a baby is born. If the heart changes and symptoms are mild, tetralogy of Fallot may not be noticed or diagnosed until adulthood.

People who are diagnosed with tetralogy of Fallot need surgery to fix the heart. They will need regular health checkups for life.


Tetralogy of Fallot symptoms depend on how much blood flow is blocked from leaving the heart to go to the lungs. Symptoms may include:

  • Blue or gray skin color.
  • Shortness of breath and rapid breathing, especially during feeding or exercise.
  • Trouble gaining weight.
  • Getting tired easily during play or exercise.
  • Irritability.
  • Crying for long periods of time.
  • Fainting.

Tet spells

Some babies with tetralogy of Fallot suddenly develop deep blue or gray skin, nails, and lips. This usually happens when the baby cries, eats or is upset. These episodes are called tet spells.

Tet spells are caused by a rapid drop in the amount of oxygen in the blood. They are most common in young infants, around 2 to 4 months old. Tet spells may be less noticeable in toddlers and older children. That's because they typically squat when they're short of breath. Squatting sends more blood to the lungs.

When to see a doctor

Serious congenital heart defects are often diagnosed before or soon after your child is born. Seek medical help if you notice that your baby has these symptoms:

  • Trouble breathing.
  • Bluish color of the skin.
  • Lack of alertness.
  • Seizures.
  • Weakness.
  • More irritable than usual.

If your baby becomes blue or gray, place your baby on the side and pull the baby's knees up to the chest. This helps increase blood flow to the lungs. Call 911 or your local emergency number immediately.


Tetralogy of Fallot occurs as the baby's heart grows during pregnancy. Usually, the cause is unknown.

Tetralogy of Fallot includes four problems with heart structure:

  • Narrowing of the valve between the heart and the lungs, called pulmonary valve stenosis. This condition reduces blood flow from the heart to the lungs. The narrowing may just involve the valve. Or it could happen in more than one place along the pathway between the heart and lungs. Sometimes the valve isn't formed. Instead, a solid sheet of tissue blocks blood flow from the right side of the heart. This is called pulmonary atresia.
  • A hole between the bottom heart chambers, called a ventricular septal defect. A ventricular septal defect changes how blood flows through the heart and lungs. Oxygen-poor blood in the lower right chamber mixes with oxygen-rich blood in the lower left chamber. The heart has to work harder to pump blood through the body. The problem may weaken the heart over time.
  • Shifting of the body's main artery. The body's main artery is called the aorta. It's usually attached to the left lower heart chamber. In tetralogy of Fallot, the aorta is in the wrong place. It's shifted to the right and sits directly above the hole in the heart wall. This changes how blood flows from the aorta to the lungs.
  • Thickening of the right lower chamber of the heart, called right ventricular hypertrophy. When the heart has to work too hard, the wall of the right lower heart chamber gets thick. Over time, this may cause the heart to become weak and eventually fail.

Some people with tetralogy of Fallot have other problems that affect the aorta or heart arteries. There also may be a hole between the heart's upper chambers, called atrial septal defect.

Risk factors

The exact cause of tetralogy of Fallot is unknown. Some things may increase the risk of a baby being born with tetralogy of Fallot. Risk factors include:

  • Family history.
  • Having a virus during pregnancy. This includes rubella, also known as German measles.
  • Drinking alcohol during pregnancy.
  • Eating poorly during pregnancy.
  • Smoking during pregnancy.
  • Mother's age older than 35.
  • Down syndrome or DiGeorge syndrome in the baby.


Untreated tetralogy of Fallot usually leads to life-threatening complications. The complications may cause disability or death by early adulthood.

A possible complication of tetralogy of Fallot is infection of the inner lining of the heart or heart valves. This is called infective endocarditis. Sometimes antibiotics are given before dental work to prevent this type of infection. Ask your healthcare team if preventive antibiotics are right for you or your baby.

Complications also are possible after surgery to repair tetralogy of Fallot. But most people do well after such surgery. When complications occur, they may include:

  • Backward flow of blood through a heart valve.
  • Irregular heartbeats.
  • A hole in the heart that doesn't go away after surgery.
  • Changes in the size of the heart chambers.
  • Swelling of part of the aorta, called aortic root dilation.
  • Sudden cardiac death.

Another procedure or surgery may be needed to fix these complications.

Congenital heart defects and pregnancy

People born with a complex congenital heart defect may be at risk for complications during pregnancy. Talk to your healthcare team about the possible risks and complications of pregnancy. Together you can discuss and plan for any special care needed.


Because the exact cause of most congenital heart defects is unknown, it may not be possible to prevent these conditions. If you have a high risk of giving birth to a child with a congenital heart defect, genetic testing and screening may be done during pregnancy.

There are some steps you can take to help reduce your child's overall risk of birth defects, such as:

  • Get proper prenatal care. Regular checkups with a healthcare team during pregnancy can help keep mom and baby healthy.
  • Take a multivitamin with folic acid. Taking 400 micrograms of folic acid daily has been shown to reduce birth defects in the brain and spinal cord. It may help reduce the risk of heart defects as well.
  • Don't drink or smoke. These lifestyle habits can harm a baby's health. Also avoid secondhand smoke.
  • Get a rubella (German measles) vaccine. A rubella infection during pregnancy may affect a baby's heart development. Get vaccinated before trying to get pregnant.
  • Control blood sugar. If you have diabetes, good control of your blood sugar can reduce the risk of congenital heart defects.
  • Manage chronic health conditions. If you have other health conditions, including phenylketonuria, talk to your healthcare team about the best way to treat and manage them.
  • Avoid harmful substances. During pregnancy, have someone else do any painting and cleaning with strong-smelling products.
  • Check with your healthcare team before taking any medications. Some medications can cause birth defects. Tell your healthcare team about all the medications you take, including those bought without a prescription.