“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.  There are times it is diagnosed later in life; it depends on the severity or the condition.”

MAYO CLINIC