How the Heart Functions

Throughout ancient history the heart was thought of as the center of our emotions, even the source of thoughts and knowledge. We still say things like good-hearted, cold-hearted, and call a story heart-rending. But only in the last 1800 years have the functions of the heart been known, and only in the last 200 years has the circulation system been understood.

It is surprising how many people, even those who know they have heart disease or those who had surgery, don't have a clear idea of how the heart works. This non-technical summary may help in understanding.

Over an average lifetime, counting only the time we are resting, the heart pumps over 50 million gallons of blood. Enough to fill 4 supertankers. If you applied the energy expended in 50 years by an average heart, it could lift over 60,000 tons, the size of a battleship, out of the water. For most of us, the heart beats about 3 million times a year. Only when the heart malfunctions or stops do we think much about it.

(Please click on the underlined terms for illustrations.)

Your heart, which is about the size of your clenched fist, is made up of four chambers, two on the left and two on the right. Each of the two upper chambers is called an atrium (both are atria, sometimes called auricles) and the two lower chambers are called ventricles. The atria receive the blood from veins and the ventricles pump the blood out to the body. The left ventricle, thicker walled than the right ventricle, sends the blood out to all parts of the body except the lungs. The right ventricle supplies only the lungs with blood. The left and right sides of the heart are separated by a half-inch thick wall of muscle, called the septum. The valves allow blood to flow in only one direction.

When the atria fill with blood from the veins returning to the heart, the valves have higher pressure above than below, and the atria contract, letting blood flow into the ventricles. The filled ventricles then contract and force the blood out through the mitral and tricuspid valves. The aortic and pulmonary valves open and snap shut, letting the blood into the aorta and pulmonary artery. As these valves snap closed, preventing blood from returning to the ventricle, the sound they make (nub-dub, nub-dub) is what we call a heartbeat. This supplies every organ in the body with life-sustaining oxygenated blood. except the heart itself. The coronary arteries are the heart's private circulatory system, fed directly from the aorta. The two main coronary arteries, right and left, branch and divide into smaller and smaller tributaries. Heart muscle would soon die if a main coronary artery became blocked and could not supply enough blood, but the smaller branches are capable of connecting with those of other arteries, providing what is called collateral circulation.

Blood, depleted in oxygen, flows from the veins into the right atrium, then to the right ventricle to be pumped through the pulmonary artery to the lungs. Oxygenated blood from the lungs flows to the left atrium, then to the left ventricle and is pumped to the aorta and to the body.

The coronary arteries start from the aorta and spread to many smaller branches that supply the heart muscles. Only the larger arteries are shown here. When plaque blocks these arteries, blood does not reach the muscles. Without oxygenated blood, muscles cannot contract to pump blood.

The valves assure the blood flows in only one direction. As the muscle contracts to pump the blood out of the chamber, the valve snaps shut, making the sound of the heartbeat.

Next: What Is Heart Disease?

©1994, 1996, 2002
Dr. Neal Pinckney
Healing Heart Foundation