What does S2 heart sound indicate?

• A. Closure of AV valves
• B. Closure of semilunar valves
• C. An abnormal heart sound
• D. Turbulent blood flow

Answer: (B)

The second heart sound comes from the closure of the semilunar valves (the aortic and pulmonary valves) at the end of systole. When these valves snap shut, the sudden stoppage of blood flow and the change in pressure produce a short, high-pitched sound. It’s often heard as two components: A2 from the aortic valve and P2 from the pulmonary valve, which can split on inspiration because the P2 valve closes slightly later. By contrast, the closure of the atrioventricular valves creates the first heart sound at the start of systole, and an abnormal sound or turbulent flow typically shows up as a murmur or extra sounds like S3 or S4, not as the normal S2. So the second heart sound specifically indicates closure of the semilunar valves.