Where is S1 loudest?

Where is S1 loudest?

• A. Apex
• B. Base
• C. Right sternal border
• D. Left lower sternal border

Answer: (A)

S1 marks the onset of systole as the mitral and tricuspid valves close, producing the loudest sound where the mitral valve closure is best heard—the apex. The apex area, around the left fifth intercostal space in the midclavicular line, is closest to the left ventricle, so this closure radiates most clearly there. Positioning the patient in the left lateral decubitus helps bring the apex closer to the chest wall and enhances low-pitched sounds, making S1 particularly prominent. In contrast, S2, from the aortic and pulmonic valves closing, is best heard at the base, so the base or right sternal border locations aren’t where S1 is typically loudest. Hence, the apex is the correct location for the loudest S1.

S1 marks the onset of systole as the mitral and tricuspid valves close, producing the loudest sound where the mitral valve closure is best heard—the apex. The apex area, around the left fifth intercostal space in the midclavicular line, is closest to the left ventricle, so this closure radiates most clearly there. Positioning the patient in the left lateral decubitus helps bring the apex closer to the chest wall and enhances low-pitched sounds, making S1 particularly prominent. In contrast, S2, from the aortic and pulmonic valves closing, is best heard at the base, so the base or right sternal border locations aren’t where S1 is typically loudest. Hence, the apex is the correct location for the loudest S1.