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.
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.
Why the silence between the Dub and the next Lub? That pause is —the heart’s rest and recharge phase. During this silence, the ventricles are relaxing, filling passively with blood from the atria. No valves are snapping shut. It’s the quietest part of the cycle. what produces the lub dub heart sounds
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."
The Lub-Dub is a brilliant evolutionary solution. It is the audible signature of one-way flow—the sound of chaos being prevented. Every snap, every thud, and every silent pause is a testament to the fact that your heart is not just a pump; it is a finely tuned, hydraulic percussion instrument. To stop this backflow, the (pulmonary and aortic) snap shut
Place your hand on the left side of your chest. Feel that? Thump-thump... thump-thump.
In fact, your heart is mostly silent during the actual pump. That’s —the actual pumping phase
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.