Which cardiac sound is produced by the closure of the semilunar valves?

• A. S1
• B. S3
• C. S2
• D. S4

Answer: (C)

Closure of the semilunar valves happens at the end of ventricular systole, when the pressure in the ventricle falls below the pressure in the aorta and pulmonary artery. That abrupt valve closure produces a short, high-pitched sound known as S2. S2 has two components: A2 from the aortic valve and P2 from the pulmonary valve; they’re usually heard together, though they can split on inspiration because the pulmonic valve closes a moment later.

In contrast, S1 is the sound of the atrioventricular valves closing at the start of systole, while S3 and S4 are extra heart sounds associated with rapid ventricular filling and atrial contraction, respectively. Therefore, the sound produced by the closure of the semilunar valves is S2.