Which heart sound is associated with the closure of the aortic and pulmonic valves and has two components (aortic closure first, then pulmonic closure)?

• A. S1 heart sound
• B. S2 heart sound
• C. S3
• D. S4

Answer: (B)

The sound described is the second heart sound, produced by the closure of the semilunar valves at the end of systole. It has two components: A2, from aortic valve closure, and P2, from pulmonic valve closure. A2 occurs slightly before P2 because the left-sided circulation reaches higher pressures and closes earlier. When these valve closures are heard together, you get S2; they can split into two distinct sounds, especially with inspiration, since increased venous return to the right heart delays the pulmonic valve closure. In contrast, S1 comes from the closure of the mitral and tricuspid valves at the start of systole, while S3 and S4 are extra sounds associated with ventricular filling and atrial contraction, respectively.