The heart is a muscular organ that pumps blood through the entire body. This job is important because blood carries oxygen and nutrients from the foods you eat and the air you breathe to all the cells in your body. Blood also carries waste products away from your cells.

What does the heart look like?

Heart valves

The heart has several valves, including valves that separate the upper and lower chambers from each other. There are also valves that separate the lower chambers of the heart from pathways that lead away from the heart. The valves of the heart include:

• The tricuspid valve. This valve separates the right atrium from the right ventricle.
• The mitral valve. This valve separates the left atrium from the left ventricle.
• The pulmonary valve. This valve separates the right ventricle from a pathway that leads to the lungs.
• The aortic valve. This valve separates the left ventricle from a pathway that leads to the rest of the body.

How does blood travel through the heart?

Blood that has traveled through the body enters the heart at the right atrium. Then the blood travels in this sequence:

1. Blood is pumped from the right atrium into the right ventricle.
2. Blood is pumped out of the heart into the lungs, where it picks up oxygen.
3. Blood re-enters the heart at the left atrium.
4. Blood is pumped into the left ventricle.
5. Blood is pumped out of the heart to the rest of the body.

How does the heart beat?

The heart beats when all the chambers of the heart squeeze (contract). The process starts when blood collects in the upper chambers of the heart. Once the chambers are full, a group of cells called the sinoatrial node sends out an electrical signal that makes the upper chambers contract. When the chambers contract, they push the blood through the tricuspid and mitral valves into the lower chambers of the heart.

Once the lower chambers have filled with blood, an electrical signal causes these chambers to contract. This pushes blood through the pulmonary and aortic valves and out of the heart.

How does activity affect the heart?

The heart beats faster and works harder when you are active. It beats more slowly and works less hard when you are resting. Your brain sends signals to the heart to meet the needs of your body.

Where to find more information

• American Heart Association: www.heart.org

Summary

• The heart is a muscular organ that pumps blood through the entire body.
• The heart is made up of four chambers.
• The heart has several valves, including valves that separate the upper and lower chambers from each other.
• The heart beats faster and works harder when you are active.
• It beats more slowly and works less hard when you are resting.