Which heart sounds signify the closing of the pulmonary and aortic semilunar valves?

The heart sounds that signify the closing of the pulmonary and aortic semilunar valves are characterized by the second heart sound, known as S2. This sound occurs at the end of systole when the ventricles have contracted and the semilunar valves close to prevent the backflow of blood into the heart as it refills during diastole.

S2 consists of two components: the closure of the aortic valve (A2) and the closure of the pulmonary valve (P2). The separation of these sounds can be audible under certain conditions, particularly during a deep inhale, making S2 an important indicator of normal cardiac function.

In contrast, S1 represents the closure of the mitral and tricuspid valves at the beginning of ventricular contraction. Diastole refers to the phase of the cardiac cycle when the heart muscle relaxes and the chambers fill with blood, but it does not specifically indicate valve closure. Premature beats are irregular heart rhythms that occur earlier than expected and are not tied to the normal cycle of valve closure. Understanding these distinctions highlights the significance of S2 in relation to the heart’s functional mechanics.