How the Heart Works
By National Heart, Lung and Blood Institute, National Institutes of Health
Heart failure is a condition in which the heart can't pump enough blood throughout the body. Heart failure does not mean that your heart has stopped or is about to stop working. It means that your heart is not able to pump blood the way that it should. The heart can't fill with enough blood or pump with enough force, or both.
Heart failure develops over time as the pumping action of the heart grows weaker. It can affect the left side, the right side, or both sides of the heart. Most cases involve the left side where the heart can't pump enough oxygen-rich blood to the rest of the body. With right-sided failure, the heart can't effectively pump blood to the lungs where the blood picks up oxygen.
The weakening of the heart's pumping ability causes:
- Blood and fluid to "back up" into the lungs
- The buildup of fluid in the feet, ankles, and legs
- Tiredness and shortness of breath
Heart failure is a serious condition. About 5 million people in the United States have heart failure, and the number is growing. Each year, another 550,000 people are diagnosed for the first time. It contributes to or causes about 300,000 deaths each year.
The heart is a muscle about the size of your fist. It works like a pump and beats 100,000 times a day.
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 blood vessels that carry blood away from the heart to the body.
The heart has four chambers or "rooms."
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.
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, which 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.
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.
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.
Other Names for Heart Failure
- Congestive heart failure or CHF (when the poor pumping function results in symptoms)
- Left-sided heart failure
- Right-sided heart failure
- Systolic heart failure
- Diastolic heart failure
The National Heart, Lung and Blood Institute (NHLBI), National Institutes of Health, "Heart Failure" section, provides leadership for a national program in diseases of the heart, blood vessels, lung, and blood; blood resources; and sleep disorders.