Which heart sound is associated with the closure of the atrioventricular valves?

The first heart sound, commonly referred to as S1, is associated with the closure of the atrioventricular (AV) valves, which include the mitral and tricuspid valves. This closure occurs at the beginning of ventricular contraction, or systole, signaling that the ventricles are about to eject blood into the aorta and pulmonary artery. The sound is typically described as a "lubb" and is significant because it marks the transition from diastole, when the heart is filling with blood, to systole, when the heart is actively pumping.

In contrast, the second heart sound, S2, is produced by the closure of the aortic and pulmonary valves at the end of systole. The third and fourth heart sounds, S3 and S4, are associated with abnormal heart function or conditions. S3 can indicate volume overload or heart failure, while S4 is typically linked to decreased ventricular compliance or increased resistance to filling due to conditions like hypertensive heart disease. Thus, the association of S1 with the closure of the AV valves is a fundamental concept in understanding the mechanics of the heart sounds during the cardiac cycle.