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The Heart and How it Works

Every part of your body needs oxygen. Your lungs take in oxygen when you breathe. It is the heart’s job to pump blood to the lungs to pick up oxygen, and then to pump this blood to every part of your body.

The heart has two independent pumping systems, one on the right side and one on the left side. Each of these systems has 2 chambers:

  • An atrium (pronounced AY-tree-um). Atria is the word used to speak of more than one atrium.
  • A ventricle (pronounced VEN-trick-ul)

The atria are located on the top of the ventricles.

The ventricles are the major pumps of the heart. The left ventricle is generally the strongest pumping part of the heart.

The heart’s atria and ventricles are connected by the heart valves. The valves are flaps that open and close to allow blood to flow from the atrium to the ventricle.

The correct direction for blood flow is from the atrium into the ventricle.

To further understand the role that each side of the heart plays in pumping blood, let’s now look at each side individually.

The right side

The right side of the heart receives blood from the veins of the body. This is “non-oxygenated” or “used” blood. The blood is referred to as used because it already has done its work, delivering oxygen to the far sites of the body before returning to the heart.

The blood is returned to the right side into the first chamber in the top portion: the right atrium. This chamber is able to expand to hold the blood volume that will fill its cavity. When there is enough blood, the tricuspid (try-CUSS-pid) heart valve allows the blood to flow into the right ventricle (the bottom part of the right side of the heart).

The main function of the right ventricle is to pump the blood to the lungs. The blood needs to return to the lungs to pick up oxygen. We sometimes say that the blood becomes “oxygenated” or “fresh” again. When the pumping action triggers the pulmonary valve, it opens. This allows the blood to flow into the lungs.

In the lungs, the blood picks up oxygen and leaves carbon dioxide behind (which you breathe out). The blood, now rich in oxygen, is sent to the left side of the heart.

The left side

The left side of the heart receives blood from the lungs. This blood is now oxygen-rich. The blood enters the left heart from special veins coming directly from the lungs (pulmonary veins).


The first chamber to receive the blood is the left atrium. As with the right side, as the atrium fills, the valve connecting the atrium and ventricle opens. This allows the blood to pass into the left ventricle.

The valve in this case is the mitral (MY-trul) valve. The left ventricle is the strongest pump of the heart. Once blood is collected in the left ventricle, it contracts and the aortic valve opens. This allows blood to pass into the ascending aorta (ay-OR-ta), the major artery that supplies blood to the entire body. After the oxygen-rich blood is used by the body, it returns to the right side of the heart, and the whole process begins again.

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