Third Heart Sound

Virtual Auscultation

patient torso with stethoscope chestpiece
patient position during auscultation

The patient's position should be supine.


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.


Heart Sounds Video

Authors and Reviewers

Authored by Dr. Jonathan Keroes, MD and David Lieberman, Developer, Virtual Cardiac Patient. Medically reviewed by Dr. Barbara Erickson, PhD, RN, CCRN. Last Update: 11/28/2021

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