The first heart sound is associated with what mechanical event of the cardiac cycle?
a. Atrioventricular valve closure
b. Atrioventricular valve opening
c. Semilunar valve closure
d. Semilunar valve opening
ANS: A
As soon as ventricular pressures exceed those in the atria, the atrioventricular valves close. Clo-sure of the mitral valve occurs first, followed immediately by closure of the tricuspid valve. This marks the end of ventricular diastole, producing the first heart sound on the phonocardiogram.
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