Guide to Heart Disease

The heart is divided into four main chambers : each one is a bag of muscles with walls that are able to contract in order to push blood out. Each wall’s thickness varies according to the amount of work it does. The walls of the left ventricle are the thickest because it does most of the pumping.
The chambers on either side of the heart are arranged in pairs. Each side has an atrium, with thin walls, to receive blood from the veins. The atrium pumps blood into a thicker-walled ventricle, through which the blood is pumped into a main artery.
The heart is involved in two separate circulatory functions. Oxygen-rich blood is pumped from the heart into the body through the aorta. This is called systemic circulation. When this blood is returned to the heart, after the cells have absorbed all the oxygen and nutrients, the heart pumps the blood into the lungs through the pulmonary artery. Here, the oxygen supply is replenished and the blood is returned to the heart. This is known as pulmonary circulation.
Pulmonary veins bring the newly-oxygenated blood from the lungs to the heart. It reaches the left atrium, which contracts and pushes the blood out through the mistral valve into the left ventricle. Then the left ventricle contracts. The blood moves through the open aortic valve into the aorta, and on to the system of arteries and capillaries, and into the tissues.

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