The first heart sound is associated with the closure of which valves and marks the onset of ventricular systole?

The first heart sound is associated with the closure of which valves and marks the onset of ventricular systole?

• A. Aortic and Pulmonic valves
• B. Mitral and Tricuspid valves
• C. Atrial and Ventricular valves
• D. None of the above

Answer: (B)

The first heart sound comes from the closure of the atrioventricular valves—the mitral and tricuspid valves—as the ventricles begin to contract. When the ventricles generate enough pressure to exceed that in the atria, these valves snap shut, producing the characteristic “lub” of S1. This moment marks the start of ventricular systole. It’s the AV valves closing that defines S1, whereas closure of the semilunar valves (aortic and pulmonic) creates the second heart sound, S2, which marks the start of diastole. There aren’t atrial valves, so the option describing those as the cause isn’t correct.