In shape man’s heart resembles his closed fist. It is located inside the chest under the left nipple. It can be felt by putting a hand on the chest or when the heart-beats become fast and more pronounced after running or in a state of great excitement.

There are arteries and veins for the distribution of blood from the heart to the entire body and again to carry back impure blood to the heart. These are spread in all parts of our body. Some of these are even thinner than hair. Those which carry the pure blood to the entire body are called arteries, and those which bring back the impure blood to the heart are called veins.

To the right of the heart is the right lung and to the left is the left lung. The heart is enclosed within a sac of muscles and tissues.

The heart is a muscular organ. It is divided into two distinct halves by a muscular wall called the septum. Each side of the heart is divided into two chambers, one above the other. These chambers are connected with thin valves, which open downwards only. The blood can flow from the upper chamber to the lower chamber, but it cannot go from the lower chamber to the upper chamber. In this way, there are four such chambers to the heart.

The heart is always at work and contracting. Its contraction and expansion are repeated in a rhythmic cycle. A short period of rest follows each contraction.

Lungs are those organs which purify the blood. After it is purified in the lungs, the blood comes back to the left receiving chamber by four veins. When this chamber gets filled, it begins to contract and the blood flows from it to the downward left chamber. The valve of the lower chamber than begins to close. When this chamber contracts, the valves closes completely, so that the blood cannot go back again to the upper chamber. After the contraction of the chamber, the blood goes to the arteries and many branches of these arteries carry it to all parts of the body.

Heart, Arteries and Veins

After pumping out the blood, the heart chambers begin to expand and soon achieve full expansion. This contraction and the closure of the valves produce distinct rhythmic sounds which are called heart-beats. The heart of the normal human adult makes 70 to 75 heart-beats in a minute. In children, the heart-beat is faster. However, in the old age it becomes slow. In one stroke, the heart pumps 60 to 80 grams of blood. It sends six kilograms of blood to the body every minute. This process continues as long as the man lives.