S2 heart sound indicates closure of which valves?

• A. AV valves
• B. Semilunar valves
• C. An abnormal heart sound
• D. Turbulent blood flow

Answer: (B)

S2 signals the closure of the semilunar valves—the aortic and pulmonary valves—at the end of ventricular systole. When the ventricles finish ejecting blood and begin to relax, their pressure falls below that of the aorta and pulmonary artery, causing those valves to snap shut. This sound is often described as two overlapping components: A2 from the aortic valve and P2 from the pulmonary valve, which can split, especially with inspiration. The other sounds you might hear relate to different events: S1 comes from the closure of the atrioventricular valves at the start of systole, and abnormal sounds or murmurs reflect pathologic conditions or turbulent flow rather than the normal valve closures. So, the second heart sound specifically reflects the semilunar valves closing.