During early diastole, the rapid filling phase of the ventricle occurs. The sound heard on auscultation that corresponds to this event in pathological states is:

• A S3 (third heart sound) — caused by sudden deceleration of blood inflow when ventricular walls become distended or non-compliant ✓
• B Opening snap — caused by the abrupt halting of mitral valve leaflet descent at full valve opening
• C S4 (fourth heart sound) — caused by atrial contraction forcing blood into a stiff ventricle in late diastole
• D Pericardial knock — early diastolic sound caused by constrictive pericardium limiting ventricular expansion

Explanation

The S3 (third heart sound) occurs at the end of rapid ventricular filling, approximately 120–180 ms after S2. It arises from sudden tensing of the ventricular walls when inflow decelerates; physiologically this may be heard in healthy young individuals with high ventricular compliance (physiological S3). Pathologically, S3 indicates ventricular volume overload or decreased compliance (dilated cardiomyopathy, mitral regurgitation, heart failure). The opening snap (option B) occurs at mitral valve opening but is caused by the sudden arrest of abnormally thick stenotic leaflets. S4 (option C) is a late diastolic sound during atrial systole, in hypertrophic or stiff ventricles. The pericardial knock (option D) can resemble S3 but has a higher frequency and occurs slightly earlier.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.