Which statement best describes the timing of S1 and S2?

Which statement best describes the timing of S1 and S2?

• A. S1 at the start of systole; S2 at the end of systole
• B. S1 during diastole; S2 during systole
• C. S1 and S2 both during systole
• D. S1 and S2 both during diastole

Answer: (A)

S1 and S2 reflect valve closures during the heart’s pumping cycle. S1 is the sound of the atrioventricular valves (mitral and tricuspid) snapping shut as the ventricles begin to contract, which is the start of systole. S2 is the sound of the semilunar valves (aortic and pulmonary) closing as the ventricles finish ejecting blood and start to relax, marking the end of systole and the beginning of diastole. So S1 occurs at the start of systole and S2 at the end of systole, with the interval between them representing the period of systole. This is why the statement describing S1 at the start of systole and S2 at the end of systole is the best choice.

S1 and S2 reflect valve closures during the heart’s pumping cycle. S1 is the sound of the atrioventricular valves (mitral and tricuspid) snapping shut as the ventricles begin to contract, which is the start of systole. S2 is the sound of the semilunar valves (aortic and pulmonary) closing as the ventricles finish ejecting blood and start to relax, marking the end of systole and the beginning of diastole. So S1 occurs at the start of systole and S2 at the end of systole, with the interval between them representing the period of systole. This is why the statement describing S1 at the start of systole and S2 at the end of systole is the best choice.