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 during infancy or soon after. However, tetralogy of Fallot might not be detected until later in life in some adults, depending on the severity of the defects and symptoms.With early diagnosis followed by appropriate surgical treatment, most children and adults who have tetralogy of Fallot live relatively normal lives, though they'll need regular medical care throughout life and might have restrictions on exercise