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Biology

Cardiac Cycle Phases and Heart Sound Generation

Quick fact

The 'lub' (S1) is caused by the closure of the mitral and tricuspid valves at the start of ventricular contraction, and the 'dub' (S2) is caused by the closure of the aortic and pulmonary valves at the end of ventricular contraction. Each heartbeat lasts about 0.8 seconds when at rest.

Why this is interesting

You've likely heard your heart's 'lub-dub' sound, but did you know those sounds are not the heart contracting? The sounds are actually the snapping shut of valves, marking the precise moments when blood flow changes direction. What do these sounds tell us about the health of your heart?