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.