Heart sounds are the noises produced by the closing of the heart valves during each heartbeat. The familiar “lub-dub” sound results from two primary events: the first sound (S1) occurs when the mitral and tricuspid valves close at the start of ventricular contraction, and the second sound (S2) occurs when the aortic and pulmonary valves close as the ventricles relax. Additional heart sounds or murmurs may indicate normal physiological variations or underlying heart disease.
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