Solution :
Heart beat
The various heart chambers expand and contract, or constrict and relax, while the heart pumps blood. A thumping sound is made whenever the chambers expand or collapse. This is what is known as the heartbeat.
A single heartbeat signals the end of a full cycle of blood pumping. A standard human heart should beat 72 times per minute. The heart pumps about 70 ml of blood with each beat. The heart can pump approximately 5 litres of blood in a minute this way. That is the beauty of the human body.