Once your blood has delivered oxygen and food to your cells, it returns to the upper chamber on the right side of your heart.

From there it moves into the lower chamber on the right side. Next, it travels to your lungs through the pulmonary artery (a short, wide blood vessel that stretches between your heart and your lungs). There, it picks up oxygen.

Once blood has picked up oxygen in the lungs, it returns to the left side of your heart through your pulmonary veins. These veins are two large blood vessels that return blood from the lungs to your heart.

Blood enters the upper chamber on the left side of the heart, and then moves into the left lower chamber. It's then pumped through the main artery of your heart (the aorta) to all parts of your body.

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.