Tetralogy of Fallot is the most common form of cyanotic congenital heart disease. The word "tetralogy" means "four components". The two major ones are: 1) a large hole, or ventricular septal defect, that allows blood to pass from the right ventricle to the left ventricle without going through the lungs, and 2) a narrowing (stenosis) at or just beneath the pulmonary valve. This narrowing partially blocks the flow of blood from the right side of the heart to the lungs. The other two components are: 3) the right ventricle is more muscular than normal, and 4) the aorta lies directly over the ventricular septal defect.

This results in cyanosis (blueness), which may appear soon after birth, in infancy or later in childhood. These "blue babies" may have sudden episodes of severe cyanosis with rapid breathing (cyanotic spells). They may even become unconscious and need urgent medical attention. During exercise, older children may become short of breath and faint. These symptoms occur because not enough blood flows to the lungs to supply the child's body with oxygen. Talk to your doctor as a matter of urgency if you think your child has tetralogy and may be having cyanotic spells.

Some infants with severe tetralogy of Fallot may need an operation to give temporary relief by increasing blood flow to the lungs with a shunt. This is achieved by making a connection between the aorta and the pulmonary artery. Then some blood from the aorta flows into the lungs to get more oxygen. This reduces the cyanosis and allows the child to grow and develop until the problem can be fixed when the child is older.

Most children with tetralogy of Fallot have open-heart surgery before school age. The operation involves closing the ventricular septal defect and removing the obstructing muscle. After surgery the long-term outlook varies, depending largely on how severe the defects were before surgery. Lifelong medical follow-up is needed.

People with tetralogy of Fallot, before and after treatment, are at risk for getting an infection within the aorta or the heart valves (endocarditis). To help prevent this, they'll need to take antibiotics before certain dental and surgical procedures.