there is one common valve. Surgery is usually conducted in-between the 3rd and 6th month of life, and with this condition the earlier the better. Usually, intracardiac repair involves closing the holes in the septum and the creation of two new atrioventricular valves from the underdeveloped common valve leaflet. See also Atrioventricular septal defect Atrioventricular septum References Embryology of cardiovascular system