Understanding Heartbeat Sounds: What Causes the "Lub-Dub"?
The heartbeat sound comes from valve closures as blood moves through the heart chambers.
- First sound (“lubb”): Closure of the atrioventricular (AV) valves (tricuspid and mitral) when ventricles contract.
- Second sound (“dupp”): Closure of the aortic and pulmonary valves when ventricular pressure drops after ejection.
This rhythmic valve opening and closing creates the characteristic lub-dub.
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