When these valves slam shut, they create vibrations in the surrounding blood and heart tissue. Your ears (or a stethoscope) detect these vibrations as sound.

Here is a deep dive into the mechanics behind the "lub-dub" and what that rhythm tells us about the health of the body’s most vital organ.

The (the S2 sound ) marks the end of systole and the beginning of diastole —the resting/filling phase.

It is caused by the simultaneous closure of the mitral and tricuspid valves (the atrioventricular valves).

The first sound, the lower-pitched and longer lub , occurs at the beginning of ventricular contraction (systole).

So the next time you feel your pulse or hear your heart in a quiet room, remember: You aren't hearing a muscle pump. You are hearing the thunderous, synchronized slam of four biological doors, closing with millisecond precision to keep you in the rhythm of life.

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