The heart works as a pump with four chambers and valves that control blood flow. Tetralogy of Fallot is a congenital heart defect combining four abnormalities: a hole between the lower chambers, narrowing of the pulmonary artery, an oversized right ventricle, and placement of the aorta over the ventricle hole. While the cause is often unknown, risks include maternal illness, alcoholism, poor nutrition or genetics. Surgical repair is required to close holes and enlarge vessels, and lifestyle changes may be needed after surgery.

15. Babies with tetralogy of Fallot will suddenly develop deep blue skin, nails and lips after crying, feeding or upon awakening. These episodes are called "Tet spells" and result from a rapid drop in the amount of oxygen in the blood.