The AV valves are invariably abnormal in patients with atrioventricular septal defects At one end of the spectrum of atrioventricular septal defects  incomplete atrioventricular septal defects  also termed ostium primum atrial septal defects (ASDs)  have only a deficiency in the inferior portion of the atrial septum immediately superior to the AV valves and have 2 valve orifices