Where is S2 best auscultated?

• A. Second intercostal space, right and left sternal borders.
• B. Second intercostal space, left sternal border, PMI.
• C. Fifth intercostal space, left sternal border, PMI.
• D. Fifth intercostal space, right sternal border, PMI.

Answer: (A)

S2 happens when the semilunar valves (aortic and pulmonic) snap shut, so the best places to hear it are where those valves are closest to the chest wall. The second intercostal space at the right sternal border corresponds to the aortic valve area, and the second intercostal space at the left sternal border corresponds to the pulmonic valve area. Hearing S2 there allows you to pick up both components—A2 on the right and P2 on the left—often with a small inspiratory split. The apex (fifth intercostal space, near the left midclavicular line) or other sites are more closely associated with S1 or other sounds, not the best locations for a clear S2. So, listening at the second intercostal space on both the right and left sternal borders provides the most reliable S2 auscultation.