S3 heart sound is often described as a gallop and is caused by ...

• A. The galloping heart, caused by blood sloshing around in a compliant left ventricle
• B. The closing of semilunar valves
• C. A sharp sound from abrupt deceleration
• D. The murmur of aortic stenosis

Answer: (A)

An S3 gallop is an extra heart sound heard in early diastole just after the second heart sound, produced by rapid filling of a very compliant ventricle. When the ventricle suddenly fills with blood from the atrium, the sudden inlet of volume makes the ventricular walls vibrate, creating the third sound. This is the sensation described as blood “sloshing around” in a compliant left ventricle. It often indicates a volume-overloaded or dilated ventricle and can be normal in younger individuals, but in older adults it can point to heart failure or other pathologies that blunt ventricular compliance.

This isn’t caused by the semilunar valves’ closure (that produces the second heart sound), nor is it the result of a sharp deceleration sound typical of S2, and it isn’t a murmur from aortic stenosis, which is a systolic murmur from turbulent blood flow across a narrowed aortic valve.