A problem in your heart's "pump system" is known as congestive heart failure. (For more details on congestive heart failure, click the button on the right.)

Let's take a closer look at how the heart's pump system works by traveling along with the blood as it makes this journey through the heart.

Blood travels throughout the body through blood vessels.

Arteries carry blood from the heart to the body. This blood is filled with oxygen and nutrients, which then are distributed in the body.

Veins carry blood from the capillaries toward the heart. All veins except the one leading from the lungs to the heart (pulmonary vein) carry unaerated blood. Unaerated blood is blood that is poor in oxygen content.

Capillaries are tiny blood vessels between arteries and veins. The capillaries help distributed oxygen and nutrients to body tissues and cells.

Blood returns to the heart through two large blood veins called inferior vena cava and superior vena cava. The inferior vena cava carries the blood from the lower body parts, the legs and feet and from organs in the abdomen and pelvis. The superior vena cava carries blood from the head and arms.

The blood from both these veins enters into a small chamber on the right side of the heart. That chamber is called the right atrium. An atrium is an upper heart chamber. Your heart has two atria (plural of atrium).

From the right atrium, blood then moves through a one-way "doorway" called the tricuspid valve into the right ventricle. Ventricle is the name for the lower heart chambers. Your heart has a total of four chambers, two upper and two lower chambers.

Once the blood enters the right ventricle, your right ventricle muscles contract and push it into the pulmonary artery. This artery takes the blood to the lungs. Inside the lungs, there is a large network of small blood vessels and air sacs where waste products and oxygen are exchanged. In other words, blood from the heart empties waste and then fills itself with oxygen.

After this exchange, the blood returns to the left atrium (left upper chamber of the heart) through the pulmonary vein. The left atrium muscle contracts and pushes the blood through another one-way valve (doorway) called the mitral valve into the left ventricle or fourth chamber of the heart. To understand how valves work, click here to watch a video.

The left ventricle is the major pumping chamber of the heart. As the muscles of the left ventricle contract, blood is pushed through a large blood vessel known as the aorta to all parts of the body. This blood contains the oxygen and nutrients that the body needs to function efficiently.

As the blood travels throughout the body, the body absorbs oxygen and nutrients and returns waste products into the blood. Once this is completed, the blood returns to the heart through the inferior and superior vena cava to start over again.

The left ventricle of the heart "ejects" or pumps a certain amount of blood each minute into the body. This amount is determined by the amount of oxygen the body needs. When you are resting, the body needs less oxygen. When you are active, the body needs more oxygen. The amount of blood the heart ejects each minute is called the cardiac output. Doctors often use the term "ejection fraction" when they measure how efficiently the heart ejects blood.