This is a graphic example of a second heart sound that is widely split in expiration and that remains widely split to the same extent in inspiration. This is called fixed splitting of S2. Wide, fixed splitting of S2 typically occurs in the presence od a large left-to-right atrial shunt produced by an atrial septal defect. Wide, fixed splitting is appreciated more easily in the standing patient, because with an atrial septal defect the splitting interval remains wide and fixed. whereas in the normal patient, standing tends to decrease the split, allowing easier identification of any respiratory variation in the splitting interval.