Family Nurse Practitioner Exam

What causes the heart sound S2?

1. Closure of the atrioventricular valves

2. Closure of the semilunar valves

3. Opening of the atrioventricular valves

4. Opening of the semilunar valves

The correct answer is: Closure of the semilunar valves

The heart sound S2, commonly referred to as the "dub," is produced by the closure of the semilunar valves, which include the aortic and pulmonary valves. During diastole, when the heart is at rest, these valves close to prevent the backflow of blood from the aorta and pulmonary artery into the ventricles after contraction. This closure creates a distinct sound that can be auscultated with a stethoscope and serves as an important indicator of the cardiac cycle phases. The timing of S2 aligns with the end of systole and the beginning of diastole, marking the transition as the ventricles relax and fill with blood. Considering the other options, the closure of the atrioventricular valves, while significant, is associated with S1, the "lub" sound, not S2. The opening of the atrioventricular or semilunar valves does not create sound in the same audible way as the closure of these valves and typically occurs during diastole and systole, respectively, without generating a significant heart sound that can be detected during routine auscultation.