Which part of the heart makes the heartbeat sound?

A heartbeat produces the familiar "LUB-DUP" sounds as the chambers contract and the valves close. The first heart sound, "lub," is heard when the ventricles contract and the atrioventricular valves close. This sound last longest and has a lower pitch. The second heart sound, "dub," is heard when the relaxation of the ventricles allows the semilunar valves to close.