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Your heart pumps blood around your body. Blood is pumped to your lungs to pick up oxygen, then flows back to your heart. The blood, with its fresh supply of oxygen, is then pumped around your body.

Your heart can pump blood around your lungs and your body at the same time because it is divided into two halves, the left and the right. (When we talk about the left or right side of your heart, we mean your left and your right.) Each half has an upper chamber and a lower chamber.

The two upper chambers of your heart are called atria. One of these chambers on its own is called an atrium. You have a left atrium and a right atrium.

The two larger chambers in the lower part of your heart are called your left and right ventricles.

Blood enters your heart through veins and leaves it through arteries. Veins and arteries run throughout your body.

Your heart pumps blood through a network of tubes that runs around your body. These tubes are your blood vessels. There are two main types of blood vessel.

• Arteries carry blood around your body after it has picked up oxygen from your lungs.
• Veins are thinner than arteries. They carry blood back from around your body after its oxygen has been used.

Blood that has delivered its food and oxygen in your body returns to your heart through two big veins on the right-hand side. The blood enters the upper chamber (the right atrium). From there, it is pumped into the lower chamber (the right ventricle). This chamber pumps the blood to your lungs through a big blood vessel called the pulmonary artery. The blood picks up oxygen in your lungs.

Carrying the oxygen, the blood returns to your heart and enters the upper chamber on the left side (the left atrium). From there, it is pumped into the lower chamber (the left ventricle) and then out again around your body.

The thump that you feel when you put your hand over the left side of your chest is your heart muscle pumping. Your heart's chambers get bigger to let blood flow into them, then get smaller to pump the blood out.

The two sides of your heart work together. As blood is pushed from the right ventricle to your lungs, the blood from the left ventricle is pumped out around your body.

Your heart beats about 60 to 80 times a minute, but this can rise to 150 times a minute if you are exercising hard.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.