In fact, your heart is mostly silent during the actual pump.
The "Lub" is the sound of the exit doors closing just as the heart tries to pump. Part 3: The "Dub" (The Escape Hatch Snap) After the "Lub," the ventricles continue to squeeze. They blast blood out through two other doors: the pulmonary valve (to the lungs) and the aortic valve (to the body). For a brief moment, the heart is emptying. what produces the lub dub heart sounds
Then comes (S2), marking the end of systole and the beginning of diastole (relaxation). In fact, your heart is mostly silent during the actual pump
And the tiny gap between the Lub and the Dub? That’s —the actual pumping phase. But again, pumping is silent. So the only reason we hear two distinct noises is because we are listening to the boundaries of the pump: the valves slamming at the start and the valves snapping at the finish. Part 5: The Party Trick (Breathing and Splitting) Here’s where it gets weird enough to impress your friends. If you listen to a child’s heart with a stethoscope and tell them to take a deep breath, the "Dub" suddenly turns into "Du-ub." It splits into two distinct sounds. They blast blood out through two other doors:
To stop this backflow, the (pulmonary and aortic) snap shut. Unlike the fleshy AV valves, these look like three tiny crescent moons (hence "semilunar") shaped like a Mercedes-Benz logo.
