Tetralogy of Fallot is a birth defect of the heart consisting of four abnormalities that results in insufficiently oxygenated blood pumped to the body. It is classified as a cyanotic heart defect because the condition leads to cyanosis, a bluish-purple coloration to the skin, and shortness of breath due to low oxygen levels in the blood. Surgery to repair the defects in the heart is usually performed between 3 and 5 years old. In more severe forms, surgery may be indicated earlier. In most cases the heart can be surgically corrected and the outcome is good.