Circulatory system circulates the blood throughout the whole body. It consists of heart, blood and blood carrying tubes. Heart pumps pure blood to different parts of the body through fine tubes called arteries.
The impure blood from different parts of the body is carried back of the heart by another kind of fine tubes called veins.
Heart is the most important and sensitive part of the body. It is situated in the chest slightly to the left side of it. It contracts and relaxes regularly. It makes a very soft sound which is called heart-beat. It can be heard by placing an ear on the chest or can be felt by placing a palm on it.
If we hold our right wrist between thumb and first two fingers of the left hand, we feel something beating. This is known as pulse. It is the indication of heart-beat.
Note: Doctors use stethoscope to measure the heart-beats.
When the heart contracts, it pumps blood into arteries and when it swells, it sucks the blood back through veins.