What Makes The | Lub Sound

As the heart's lower chambers (ventricles) begin to contract, the pressure inside them rises rapidly.

– From the classic lub-dub of heart valves closing (atrioventricular valves slamming shut = lub) to the sound of a cork being pulled from a bottle, or even the acoustics of a plunger in a syringe. No matter which “lub” brought you here, it’s addressed.

To provide context for the "lub," it is necessary to briefly describe the "dub."