S2 heart sound corresponds to the closure of which valves?

• A. Closure of AV valves
• B. Closure of semilunar valves
• C. Opening of AV valves
• D. Opening of semilunar valves

Answer: (B)

S2 is produced when the semilunar valves—the aortic and pulmonic valves—close at the end of ventricular systole, stopping backflow into the ventricles. This marks the end of ejection. By contrast, S1 comes from the closure of the atrioventricular valves at the start of systole, and opening of valves does not create these heart sounds. In normal physiology, S2 has two components, A2 and P2, which can produce a split sound with inspiration. The key point is that S2 reflects the closure of the semilunar valves.