How the Heart Works

The heart is a muscle about the size of your fist. The heart works like a pump and beats about 100,000 times a day.

A healthy adult heart generally beats 60 to 100 times a minute, but it can beat faster or slower at times. For example, physical activity, strong emotion, certain medicines, fever, or infection can make the heart beat faster. A person's heart rate generally slows down during sleep. Some very fit athletes always have heart rates below 60 beats a minute because their hearts work so well.

The heart has two sides, separated by an inner wall called the septum. The right side of the heart pumps blood to the lungs to pick up oxygen. Then, oxygen-rich blood returns from the lungs to the left side of the heart, and the left side pumps it to the body.

The heart has four chambers and four valves and is connected to various blood vessels. Veins are the blood vessels that carry blood from the body to the heart. Arteries are the vessels that carry blood away from the heart to the body.

Heart Chambers

The heart has four chambers or "rooms"—two on the left side of the heart and two on the right.

  • The atria are the two upper chambers that collect blood as it comes into the heart.
  • The ventricles are the two lower chambers that pump blood out of the heart to the lungs or other parts of the body.

Heart Valves

Four valves control the flow of blood from the atria to the ventricles and from the ventricles into the two large arteries connected to the heart.

  • The tricuspid valve is in the right side of the heart, between the right atrium and the right ventricle.
  • The pulmonary valve is in the right side of the heart, between the right ventricle and the entrance to the pulmonary artery that carries blood to the lungs.
  • The mitral valve is in the left side of the heart, between the left atrium and the left ventricle.
  • The aortic valve is in the left side of the heart, between the left ventricle and the entrance to the aorta, the artery that carries blood to the body.

Valves are like doors that open and close. They open to allow blood to flow through to the next chamber or to one of the arteries, and then they shut to keep blood from flowing backward.

When the heart's valves open and close, they make a "lub-DUB" sound that a doctor can hear using a stethoscope.

  • The first sound—the "lub"—is made by the mitral and tricuspid valves closing at the beginning of systole. Systole is when the ventricles contract, or squeeze, and pump blood out of the heart.
  • The second sound—the "DUB"—is made by the aortic and pulmonary valves closing at beginning of diastole. Diastole is when the ventricles relax and fill with blood pumped into them by the atria.

Arteries

The arteries are major blood vessels connected to your heart.

  • The pulmonary artery carries blood pumped from the right side of the heart to the lungs to pick up a fresh supply of oxygen.
  • The aorta is the main artery that carries oxygen-rich blood pumped from the left side of the heart out to the body.
  • The coronary arteries are the other important arteries attached to the heart. They carry oxygen-rich blood from the aorta to the heart muscle, which must have its own blood supply to function.

Veins

The veins are also major blood vessels connected to your heart.

  • The pulmonary veins carry oxygen-rich blood from the lungs to the left side of the heart so it can be pumped out to the body.
  • The vena cava is a large vein that carries oxygen-poor blood from the body back to the heart.

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