The "lub dub" is the sound of your heart valves closing like doors. Here’s a short story to remember it: Lub-Dub’s Little Door Every time your heart beats, two pairs of tiny doors snap shut in perfect sequence. — the tricuspid and mitral valves close first, trapping blood in the ventricles like a fist squeezing. Dub — a split-second later, the pulmonary and aortic valves slam shut, pushing blood out to your lungs and body. That pause between them? Your heart muscle resting for just 0.3 seconds before it all starts again. So the next time you press your ear to a friend’s chest (or your own), you’re listening to a two-step rhythm: close-hold, push-rest . That’s your life’s drumbeat. No microphones, no strings — just four tiny doors and a muscle that never sleeps.

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what is the lub dub sound in your heart