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The heart: All you need to know

The human heart is a finely-tuned instrument that serves the whole body. It is a muscular organ around the size of a closed fist, and it sits in the chest, slightly to the left of center.

The heart beats around 100,000 times a day, pumping approximately 8 pints of blood throughout the body 24/7. This delivers oxygen- and nutrient-rich blood to tissues and organs and carries away waste.

The heart sends deoxygenated blood to the lungs, where the blood loads up with oxygen and unloads carbon dioxide, a waste product of metabolism.

Together, the heart, blood, and blood vessels — arteries, capillaries, and veins — make up the circulatory system.

Anatomy of the heart

Below is an interactive 3D model of the heart. Explore the model using your mouse pad or touchscreen to learn more.

The heart consists of four chambers:

  • The atria: These are the two upper chambers, which receive blood.
  • The ventricles: These are the two lower chambers, which discharge blood.

A wall of tissue called the septum separates the left and right atria and the left and right ventricle. Valves separate the atria from the ventricles.

How the heart works

The rate at which the heart contracts depends on many factors, such as:

  • activity and exercise
  • emotional factors
  • some medical conditions


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