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 filtere out by the kidneys, liver, and lungs.
The heart performs its task through the collaborative efforts of three components:
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.
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.
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.