Which valve event produces the major component of the first heart sound (S1)?

• A Closure of the aortic and pulmonary valves
• B Closure of the mitral valve, which precedes tricuspid closure ✓
• C Closure of the tricuspid valve, which precedes mitral closure
• D Opening of the mitral valve at the start of rapid filling

Explanation

S1 marks the onset of ventricular systole and is generated mainly by closure of the atrioventricular valves. Because left ventricular pressure rises faster than right ventricular pressure, the mitral valve closes slightly before the tricuspid valve, producing audible splitting of S1 in some subjects. The aortic and pulmonary valves close later and produce S2, while mitral opening occurs during early diastole and contributes to the third heart sound.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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