S3 heart sound is best described as which of the following?

• A. Early-diastolic reverberation caused by a dilated left ventricle
• B. Late-diastolic reverberation caused by a stiff left ventricle
• C. Opening of the mitral valve
• D. Closing of the aortic valve

Answer: (A)

The main feature being tested is the ventricular gallop created by rapid passive filling of the ventricle in early diastole. An S3 is a low-frequency sound that follows the second heart sound and results from the sudden deceleration of blood entering a compliant ventricle, often when the ventricle is dilated or volume-overloaded. It’s classically described as an early-diastolic reverberation due to this rapid filling into a left ventricle that can be dilated or have reduced compliance. It’s best heard with the bell at the apex in the left lateral decubitus position, often during expiration, and may be normal in children and young, healthy individuals or indicate systolic heart failure in adults.

This fits the description of an early diastolic event associated with a dilated ventricle. By contrast, a late-diastolic sound would point to a stiff ventricle (S4) due to atrial contraction against a noncompliant ventricle, opening of the mitral valve would be an opening snap, and closing of the aortic valve corresponds to S2.