Which heart sound marks the onset of systole?

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Multiple Choice

Which heart sound marks the onset of systole?

Explanation:
The onset of systole is marked by the closure of the atrioventricular valves (mitral and tricuspid), producing the first heart sound—the familiar "lub." This sound occurs as the ventricles begin to contract and push blood into the aorta and pulmonary artery. The second heart sound, the "dub," comes later, at the end of systole, when the semilunar valves close. S3 and S4 are extra sounds associated with filling phases and atrial contraction, not the start of systole. So the first heart sound best represents the beginning of systole.

The onset of systole is marked by the closure of the atrioventricular valves (mitral and tricuspid), producing the first heart sound—the familiar "lub." This sound occurs as the ventricles begin to contract and push blood into the aorta and pulmonary artery. The second heart sound, the "dub," comes later, at the end of systole, when the semilunar valves close. S3 and S4 are extra sounds associated with filling phases and atrial contraction, not the start of systole. So the first heart sound best represents the beginning of systole.

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