Tetralogy of Fallot (teh-TRAL-uh-jee of fuh-LOW) is a rare condition caused by a combination of four heart defects that are present at birth (congenital).

These defects, which affect the structure of the heart, cause oxygen-poor blood to flow out of the heart and to the rest of the body. Infants and children with tetralogy of Fallot usually have blue-tinged skin because their blood doesn't carry enough oxygen.

Tetralogy of Fallot is often diagnosed while the baby is an infant or soon after. Sometimes, depending on the severity of the defects and symptoms, tetralogy of Fallot is not detected until adulthood.

All babies who have tetralogy of Fallot need corrective surgery. People with tetralogy of Fallot need regular doctor's checkups for the rest of their life and may have activity restrictions.

Tetralogy of Fallot


Tetralogy of Fallot symptoms vary, depending on the amount of blood flow that's blocked. Signs and symptoms may include:

  • A bluish coloration of the skin caused by low blood oxygen levels (cyanosis)
  • Shortness of breath and rapid breathing, especially during feeding or exercise
  • Poor weight gain
  • Tiring easily during play or exercise
  • Irritability
  • Prolonged crying
  • Heart murmur
  • Fainting
  • An abnormal, rounded shape of the nail bed in the fingers and toes (clubbing)

Tet spells

Sometimes, babies who have tetralogy of Fallot will suddenly develop deep blue skin, nails and lips after crying or feeding, or when agitated.

These episodes are called tet spells. Tet spells are caused by a rapid drop in the amount of oxygen in the blood. Tet spells are most common in young infants, around 2 to 4 months old. Toddlers or older children might instinctively squat when they're short of breath. Squatting increases blood flow to the lungs.

When to see a doctor

Seek medical help if you notice that your baby has the following signs or symptoms:

  • Difficulty breathing
  • Bluish discoloration of the skin
  • Passing out or seizures
  • Weakness
  • Unusual irritability

If your baby becomes blue (cyanotic), place your baby on his or her side and pull your baby's knees up to his or her 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 is developing during pregnancy. Usually, the cause is unknown.

Tetralogy of Fallot includes four defects:

  • Narrowing of the lung valve (pulmonary valve stenosis). Narrowing of the valve that separates the lower right chamber of the heart (right ventricle) from the main blood vessel leading to the lungs (pulmonary artery) reduces blood flow to the lungs. The narrowing might also affect the muscle beneath the pulmonary valve. Sometimes, the pulmonary valve doesn't form properly (pulmonary atresia).
  • A hole between the bottom heart chambers (ventricular septal defect). A ventricular septal defect is a hole in the wall (septum) that separates the two lower chambers of the heart (left and right ventricles). The hole causes oxygen-poor blood in the right ventricle to mix with oxygen-rich blood in the left ventricle. This causes inefficient blood flow and reduces the supply of oxygen-rich blood to the body. The defect eventually can weaken the heart.
  • Shifting of the body's main artery (aorta). Normally the aorta branches off the left ventricle. In tetralogy of Fallot, the aorta is in the wrong position. It's shifted to the right and lies directly above the hole in the heart wall (ventricular septal defect). As a result, the aorta receives a mix of oxygen-rich and oxygen-poor blood from both the right and left ventricles.
  • Thickening of the right lower heart chamber (right ventricular hypertrophy). When the heart's pumping action is overworked, the muscular wall of the right ventricle becomes thick. Over time this might cause the heart to stiffen, become weak and eventually fail.

Some children or adults who have tetralogy of Fallot may have other heart defects such as a hole between the heart's upper chambers (atrial septal defect), a right aortic arch or problems with the coronary arteries.

Risk factors

While the exact cause of tetralogy of Fallot is unknown, some things might increase the risk of a baby being born with this condition. Risk factors for tetralogy of Fallot include:

  • A viral illness during pregnancy, such as rubella (German measles)
  • Drinking alcohol during pregnancy
  • Poor nutrition during pregnancy
  • A mother older than age 40
  • A parent who has tetralogy of Fallot
  • The presence of Down syndrome or DiGeorge syndrome in the baby


A possible complication of tetralogy of Fallot is infection of the inner lining of the heart or heart valve caused by a bacterial infection (infective endocarditis). Your or your child's doctor may recommend taking antibiotics before certain dental procedures to prevent infections that might cause this infection.

People with untreated tetralogy of Fallot usually develop severe complications over time, which might result in death or disability by early adulthood.

Complications from tetralogy of Fallot surgery

While most babies and adults do well after open-heart surgery to repair tetralogy of Fallot defects (intracardiac repair), long-term complications are common. Complications may include:

  • Leaking pulmonary valve (chronic pulmonary regurgitation), in which blood leaks through the valve back into the pumping chamber (right ventricle)
  • Leaking tricuspid valve
  • Holes in the wall between the ventricles (ventricular septal defects) that may continue to leak after repair or may need re-repair
  • Enlarged right ventricle or left ventricle that isn't working properly
  • Irregular heartbeats (arrhythmias)
  • Coronary artery disease
  • Enlargement of the ascending aorta (aortic root dilation)
  • Sudden cardiac death

It's very important to have regular checkups with a heart doctor trained in caring for people with congenital heart disease (pediatric cardiologist or adult congenital cardiologist).

Tetralogy of Fallot care at Mayo Clinic

Aug. 17, 2021
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