Which heart sound indicates the beginning of diastole?

The second heart sound (S2) is associated with the closure of the aortic and pulmonary valves, marking the end of systole and signaling the beginning of diastole. When the heart relaxes after contraction, the ventricles fill with blood; this relaxation phase is crucial for allowing the heart to receive blood from the atria and is reflected in the timing of the heart sounds.

S1, the first heart sound, occurs at the beginning of systole when the atrioventricular valves close. The third and fourth heart sounds (S3 and S4) are related to abnormal filling and can reflect over-distension or stiffening of the ventricles, but they do not denote the transition into diastole. Therefore, the identification of S2 as signifying the start of diastole is accurate in the context of heart sounds and cardiac cycles.