A third heart sound (S3) occurs early in diastole, just after the second heart sound. S3 is a low-frequency sound best heard using the bell of the stethoscope pressed lightly on the skin of the chest. Position the chestpiece at the left lateral sternal border (LLSB) or xiphoid area.
Sudden deceleration of blood flow into the left ventricle from the left atrium causes the third heart sound. In the anatomy video, observe the thin-walled, dilated left ventricle with generalized decreased vigor of contraction.
In the presence of a third heart sound (S3), the first heart sound decreases in intensity while the second heart sound increases in intensity
In young people and athletes, it is a normal phenomenon. In older individuals, it indicates the presence of heart disease.
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The patient's position is supine.
