What produces the S2 heart sound?

• A. Closure of the aortic valve
• B. Closure of the mitral valve
• C. Closure of the tricuspid valve
• D. Closure of the pulmonic valve

Answer: (A)

Second heart sound comes from the abrupt closure of the semilunar valves at the end of ventricular systole. This sound has two parts: A2 from the aortic valve and P2 from the pulmonic valve. The closure of these valves marks the end of ejection and the onset of diastole, producing the characteristic “dub.” Often the aortic component is louder and heard at the base, while the pulmonic component can be softer and may split with inspiration. The mitral and tricuspid valves close at the start of systole to form the first heart sound, not the second. Among the options, the closure of the aortic valve aligns with producing S2, since it is one of the semilunar valves responsible for this second heart sound.