What heart sound is generally referred to as S2?

The heart sound commonly referred to as S2 is the result of the closure of the semilunar valves, specifically the aortic and pulmonary valves, at the end of ventricular systole. This occurs when the pressure in the ventricles falls below the pressure in the aorta and pulmonary artery, prompting these valves to close. The sound associated with this closure is often described as a "dub," which follows the S1 heart sound (the "lub") produced by the closure of the atrioventricular valves.

Understanding this mechanism is crucial for interpreting heart sounds during auscultation and recognizing their significance in various cardiac conditions. The distinction between S1 and S2 is a fundamental aspect of cardiac physiology and pathology.