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How the heart works

Your heart is a pump. It’s a muscular organ about the size of your fist, situated slightly left of center in your chest. Your heart is divided into the right and the left side. The division protects oxygen-rich blood from mixing with oxygen-poor blood. Oxygen-poor blood returns to the heart after circulating through your body.


  • The right side of the heart, comprising the right atrium and ventricle, collects and pumps blood to the lungs through the pulmonary arteries.
  • The lungs refresh the blood with a new supply of oxygen. The lungs also breathe out carbon dioxide, a waste product.
  • Oxygen-rich blood then enters the left side of the heart, comprising the left atrium and ventricle.
  • The left side of the heart pumps blood through the aorta to supply tissues throughout the body with oxygen and nutrients.

Heart valves

Four valves within your heart keep your blood moving the right way by opening only one way and only when they need to. To function properly, the valve must be formed properly, must open all the way and most close tightly so there’s no leakage. The four valves are:


  • Tricuspid
  • Mitral
  • Pulmonary
  • Aortic

Heartbeats

A beating heart contracts and relaxes in a continuous cycle.


  • During contraction (systole), your ventricles contract, forcing blood into the vessels to your lungs and body.
  • During relaxation (diastole), the ventricles are filled with blood coming from the upper chambers (left and right atria).