Which heart sound occurs when the aortic and pulmonic valves close at the onset of diastole?

The heart sound that occurs when the aortic and pulmonic valves close at the onset of diastole is known as S2. This sound is a result of the closure of the semilunar valves (aortic and pulmonic) and it marks the end of ventricular systole and the beginning of ventricular diastole.

Understanding the timing of heart sounds is crucial in cardiology and physiology. S1 occurs when the mitral and tricuspid valves close at the beginning of ventricular systole, signaling the start of the heartbeat cycle. S3 and S4 are additional heart sounds associated with specific cardiac events; S3 is often associated with rapid ventricular filling and may indicate heart failure in some contexts, while S4 is associated with atrial contraction and is typically seen in conditions of decreased ventricular compliance.

Thus, S2 is specifically recognized as the sound of the closure of the aortic and pulmonic valves, clearly defining the transition into diastolic relaxation of the heart.