The Heart

The heart is one of the vital organs in the body located within the chest. Its mainly composed of muscle and pumps blood throughout the body. The size of the heart varies from person to person. It is roughly the size of a clenched fist. The heart is considered a vital organ in that if it is severely diseased or injured, death can occur sometimes within minutes.


The heart has 4 chambers – 2 on the right and 2 on the left. The chambers that receive incoming blood are known as the atria (plural of atrium). The chambers that pump out blood are known as the ventricles.

The right side of the heart is made up of the right atrium and right ventricle. Blood that is low in oxygen enters the right atrium through the inferior and superior vena cava (veins), is pushed into the right ventricle and the pumped out to the lungs via the pulmonary artery.

At the lungs the blood receives oxygen and disposes of carbon dioxide.

The left side of the heart is made up of the left atrium and left ventricle. The left atrium receives oxygen-rich blood from the pulmonary veins, passes it to the left ventricle and then pumps it out to the rest of the body through the aorta.


There are four heart valves which prevent backward flow of blood. This ensures that blood only flows in one direction – from an atrium into a ventricle and out of the heart. These four valves can be divided into two sets :

  • two atrioventricular (AV) valves that separate the atrium and ventricle on each side, and
  • two semilunar valves between the ventricles and arteries that carry blood out of the heart.

The atrioventricular valves include the tricuspid valve between the right atrium and right ventricle, and the bicuspid (mitral) valve between the left atrium and left ventricle.

The semilunar valves are include the aortic and pulmonary valves. The aortic valve lies between the left ventricle and aorta while the pulmonary valve lies between the right ventricle and pulmonary artery.

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