The heart has four chambers in a series, which pump the blood collected from the body to the lungs and then receive the purified blood (filled with oxygen) from the lungs and again pump the same to the whole body. These chambers are called right atrium (RA), right ventricle (RV), left atrium (LA) and left ventricle (LV). For a better understanding let’s call them chambers 1, 2, 3 and 4.

‘Chamber 1′ gets about 70 millilitres of blood almost every second from the entire body through two major veins (tubes carrying blood to the heart). This blood accumulates and is passed on to ‘chamber 2′ through a valve which opens only in one direction allowing the collected blood to pass in that direction. ‘Chamber 2′ contracts, thereby closing the valve between the first and second chambers, but opening another valve which pushes 70 ml. blood to both the lungs.

The blood now reaches the lungs for purification i.e. removal of carbon dioxide and filling up with oxygen. The lungs collect oxygen from the air that we breathe in through the nose.

Once the blood is purified it is sent to ‘chamber 3′ through some tubes and accumulates there. Then this blood is pushed to ‘chamber 4′ through another valve which only opens in the direction of ‘chamber 4′. No sooner the blood reaches ‘chamber 4′ this valve closes.

‘Chamber 4′ is the strongest and the most useful chamber of the heart as it has to pump blood to the entire body. Once the 70 ml. of blood comes to ‘chamber 4′, it contracts vigorously resulting in building a high pressure (above 120 mm of mercury). This opens another valve and pushes the blood to the main artery of the body called the aorta. Since the blood pressure inside the aorta is about 120 mm of mercury (mmHg), ‘chamber 4′ has to create a pressure of more than 120 mmHg to push the blood into this tube. The aorta now branches and re-branches to supply this blood to the entire body.

The first branch that the aorta gives blood goes to the heart, Usually two branches are available to the heart  -  one on the right and another on the left to supply blood to the heart muscles, especially the muscles of ‘chamber 4′. These two branches – the right coronary artery and the left coronary artery (more popularly called left main) divide and re-divide to supply the blood that they get from the aorta to the heart muscles. Immediately after its origin, the left main divides into two branches called left anterior descending (LAD) and left circumflex (LCx) to supply to the left part of the heart.

The condition of the heart is like that of a cashier in the bank. The cashier handles crores (one crore is equal to 10 million) of money everyday, but he cannot use it for himself or for his personal requirements. He has to depend on his own salary which forms a small part of the cash that he is handling. Likewise the heart also handles so much blood everyday through its chambers but can utilize only a fraction of it for its own use.

One must remember that once all the chambers of the heart contract a round, 70 ml. of blood is pushed. Since the heart chambers contract 72 times in a minute, a total of about 5000 ml. of blood is pushed to the whole body in 72 installments.

The aorta, supplying blood, first circulates the blood to the entire body. It immediately gives a branch on the right side to supply blood to the whole of the right hand. The next branches are to the brain and left hand. It takes a turn below, and gives a series of branches, called arteries to the chest walls. Once it enters the abdomen it supplies blood to the liver, kidneys, spleen and intestines (both large and small). Finally it divides into two branches to supply blood to the legs.

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