The first heart sound is due to the closure of which valves?

The first heart sound is due to the closure of which valves?

• A. Atrioventricular valves (mitral and tricuspid)
• B. Semilunar valves (aortic and pulmonary)
• C. Aortic valve only
• D. Pulmonary valve only

Answer: (A)

The first heart sound comes from the closure of the atrioventricular valves—the mitral on the left and the tricuspid on the right—at the start of ventricular systole. When the ventricles begin to contract, their pressure rises above the atria, causing these valves to snap shut. The vibration of the valve leaflets and supporting structures during this closure produces the lub sound. This timing marks the onset of systole and is often best heard at the apex. In contrast, the second heart sound comes from the abrupt closing of the semilunar valves (aortic and pulmonary) at the end of systole.

The first heart sound comes from the closure of the atrioventricular valves—the mitral on the left and the tricuspid on the right—at the start of ventricular systole. When the ventricles begin to contract, their pressure rises above the atria, causing these valves to snap shut. The vibration of the valve leaflets and supporting structures during this closure produces the lub sound. This timing marks the onset of systole and is often best heard at the apex. In contrast, the second heart sound comes from the abrupt closing of the semilunar valves (aortic and pulmonary) at the end of systole.