What Produces The Lub Dub Heart Sounds //top\\ May 2026

Place your hand on the left side of your chest. Feel that? Thump-thump... thump-thump.

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

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. Place your hand on the left side of your chest

In fact, your heart is mostly silent during the actual pump. thump-thump

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.

For most of us, it’s the most reliable metronome we’ll ever own. We call it a heartbeat, but in medical terms, it’s known as the . It’s so familiar that we rarely question it. We assume the sound is simply the heart contracting like a fist squeezing blood.

But the truth is far stranger and more fascinating. The "Lub-Dub" isn't the sound of muscle flexing. It’s not blood rushing through pipes. And it’s definitely not the heart "pumping."