S3 in heart sounds is best described as?

• A. A normal heart sound
• B. A type of murmur
• C. An abnormal heart sound
• D. Closure of AV valves

Answer: (C)

S3 is an extra heart sound that follows the second heart sound, reflecting abnormal ventricular filling dynamics. It arises from rapid early diastolic filling of a ventricle that is volume overloaded or dilated, causing vibrations of the ventricular walls and structures. In adults, this pattern is typically considered abnormal because it points to elevated filling pressures or heart failure; in children or young people it can be a normal finding (physiologic S3). It is not one of the normal valve-closure sounds (that is S1), and it is not a murmur, which is a turbulent flow sound. Clinically, it’s best detected with the bell at the apex in the left lateral decubitus position during quiet conditions.