Split S2

     The sound you are hearing now is a normal sinus rhythm with a splitting of S2. In this case, the splitting is due to a normal physiologic cause: respiration. In most healthy adults, a splitting of S2 can be heard during deep inspiration. The reason for this relates to the fact mentioned in the murmur overview discussion that the second heart sound is actually a blending of the closing sounds of two distinct heart valves. Normally, the aortic valve closes just before the pulmonary valve, but they are so close together that the sound is a uniform and instantaneous S2. When a person takes in a deep breath, the decrease in intrathoracic pressure causes an increase in venous return. This causes the right atrium and ventricle to fill slightly more than normal, and it takes the ventricle slightly longer during systole to eject this extra blood. This delay in ejection forces the pulmonary valve to stay open a bit longer than usual, and the normally small difference between aortic and pulmonary valve closure becomes noticeable as a split S2.

     Normally, a patientís heart would cycle between a normal and split S2 as inspiration occurs. Because this sound is looped for playback, you are hearing only the split S2. If this were the actual sound pattern you heard when auscultating, this would be a fixed, split S2, which is not a normal condition and is associated with atrial septal defects.