The heart is a muscle, about the size of a clenched fist. It is responsible for pumping blood throughout the body, every second of every day. The circulating blood delivers oxygen and nutrients to the body’s organs and tissues, and drops off waste products to be filtered out by the kidneys, liver and lungs.

The heart performs its task through the collaborative efforts of three components:

• The heart structure (the muscle's chambers and valves)
• The electrical system (the signals that tell the heart to beat)
• The circulatory system (the blood pathways)

The Heart Structure

The heart muscle is divided into four chambers — the left and right atria (the upper chambers) and the left and right ventricles (the lower chambers). With each heartbeat, the atria draw blood into the heart and send it on to the ventricles, which push the blood out of the heart. Valves located between the chambers and at the ends of the ventricles, open and close like doorways to make sure the blood continues to move forward in the right direction.

The Electrical System

What keeps the heart pumping is a built-in electrical system. An electrical impulse generator, called the “sinus node,” sends signals from the right atrium to trigger the heartbeat, like a natural pacemaker. The electrical current follows a web of pathways through the heart, causing the chambers to squeeze and release in a steady, rhythmic sequence that draws blood into the heart and pushes it out.

The Circulatory System

Arteries are the vessels that carry “fresh” blood, rich in oxygen, from the left side of the heart to smaller vessels, called capillaries, throughout the body. Veins return “used” blood from the capillaries to the right side of the heart, which routes it to the lungs to pick up fresh oxygen. The fresh blood then returns to the left side of the heart, and the cycle repeats.

During each heartbeat, the heart contracts and relaxes. When your heart contracts, it pushes blood out of the two pumping chambers (ventricles). When your heart relaxes, the ventricles refill with blood. The term “ejection fraction” refers to the percentage of blood that’s pumped out of a filled ventricle with each heartbeat. This percentage helps your healthcare provider determine if you have heart failure or other kinds of heart disease. Learn more about ejection fraction (EF) and understanding your EF number »

When Things Don’t Work Together

Click the image to see an animation on common heart problems.

Trouble in any part of the heart’s components can disrupt the entire system and lead to problems elsewhere. For instance, a clogged artery can cause a heart attack, which can damage a part of the heart muscle, which can disrupt the electrical pathway in the damaged area, which can cause a disturbance in the heart rhythm (an arrhythmia).

Keeping Things Running Smoothly

Keeping this interrelated system healthy is largely under your control. Following the commonly prescribed advice to eat well, exercise, avoid excess alcohol and refrain from smoking can go a long way toward maintaining good heart health. However, some heart problems can occur despite the best efforts to stay healthy. Ongoing research continues to lead to new medicines, procedures and interventions to help minimize heart problems and keep the whole system running smoothly.