Which heart sound coincides with the R wave on an EKG?

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Multiple Choice

Which heart sound coincides with the R wave on an EKG?

The timing of heart sounds with the cardiac cycle shows that the first heart sound comes from closure of the mitral and tricuspid valves as the ventricles begin to contract. This occurs right as ventricular depolarization starts, which on the EKG is the QRS complex, especially the R wave. So the sound you hear as the “lub” lines up with the R wave because it marks the onset of ventricular systole and AV valve closure. The other sounds have different timing: the second heart sound is from the closure of the aortic and pulmonary valves at the end of systole, around the T wave; the third heart sound (S3) happens in early diastole during rapid filling, and the fourth heart sound (S4) occurs late in diastole with atrial contraction against a stiff ventricle.

The timing of heart sounds with the cardiac cycle shows that the first heart sound comes from closure of the mitral and tricuspid valves as the ventricles begin to contract. This occurs right as ventricular depolarization starts, which on the EKG is the QRS complex, especially the R wave. So the sound you hear as the “lub” lines up with the R wave because it marks the onset of ventricular systole and AV valve closure.

The other sounds have different timing: the second heart sound is from the closure of the aortic and pulmonary valves at the end of systole, around the T wave; the third heart sound (S3) happens in early diastole during rapid filling, and the fourth heart sound (S4) occurs late in diastole with atrial contraction against a stiff ventricle.

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