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.
But sound needs vibration, and muscle contraction is a relatively smooth, slow process. It generates almost no audible noise. If you could stand inside a healthy heart during a beat, you wouldn’t hear a "crunch" or a "squeeze." You’d hear... silence, followed by chaos. what produces the lub dub heart sounds
The "Dub" is the sound of the escape hatches closing after the blood has left. Part 4: The Bizarre Physics of the Silent Gap Notice the rhythm: Lub...Dub...pause...Lub...Dub...pause. The "Lub" is the sound of the exit