The human heart is an astonishing organ. A muscle only about the size of your fist, it sits just to the left of the center of your chest contracting and relaxing to pump blood -- roughly five liters of it a minute -- throughout your body. It is an involuntary muscle. Unlike, for example, the muscles in your arm that you flex voluntarily when you lift something, your heart needs no instruction. It operates independently and continuously, day and night, week in, week out, year after year. When it stops, life stops.
What Is Heart Disease?
The heart is tough, but it's not invulnerable and it can be afflicted by a variety of diseases. But what's commonly called heart disease (though, more accurately known as "coronary artery disease") is, interestingly enough, not a disease of the heart at all. At least not directly. It's a disease of the large arteries outside the heart that supply the smaller vessels that feed the heart muscle with blood rich in nutrients and oxygen that the heart needs to keep working. Other vessels carry away the waste products produced by the heart in the course of its work. Coronary arteries, the large arteries carrying blood to the heart muscle, are like the huge pipes that carry water from a reservoir to a big city, to be distributed to streets, individual houses, and then specific faucets before being carried away again through drains. If something happens to those big pipes that blocks the flow of vital water to the city, the city shuts down in no time at all. Your heart needs an open system of pipes to maintain an unabated flow of blood all the time.
When the heart works harder, such as during exertion or stress, it needs even more blood flow. It gets this greater flow because, unlike water pipes, the blood vessels can dilate, or open larger, when the need arises. When something impedes that flow, it causes immediate problems for the heart muscle, which becomes starved of oxygen and nutrients.
With heart disease, the "something" that restricts the flow is an accumulation of fatty deposits -- including cholesterol -- that form thick "plaques" on the interior walls of the coronary arteries, a process that can slow the flow of blood to the heart. This condition, called atherosclerosis, occurs gradually and may go unnoticed for years.
What Are the Symptoms of Heart Disease?
When atherosclerosis is advanced, the flow of blood can be reduced enough that when the heart is asked to work harder than usual -- for example, when you're exercising or climbing stairs, or simply digesting a heavy meal -- it can't get the blood flow that it needs.
Typically, the heart signals that it's struggling by producing a feeling of chest discomfort, a condition that doctors call angina. Angina can take many forms; the sensations can include weakness, heaviness, pressure, tightness, and even pain in the middle of the chest. People with angina may also feel this discomfort at some distance from the heart -- in the arms, abdomen, back, neck, and lower jaw, for example. Angina is simply the heart's way of saying there is a mismatch between the oxygen-rich blood flow it needs and what is actually arriving for its use. Usually, if you have this symptom, the discomfort goes away when you stop whatever activity is causing your heart to work harder than usual (or, if you've already been diagnosed with angina, when you take medication, such as nitroglycerin tablets or spray). You should also know that not everyone has this feeling when there is a problem with blood flow to the heart, but it usually is an important signal when it occurs.
Harlan M. Krumholz, M.D., is a professor of cardiology, epidemiology, and public health at the Yale University School of Medicine and director of the Yale-New Haven Hospital Center for Outcomes Research and Evaluation. Author of more than 250 journal articles, Dr. Krumholz serves on numerous cardiovascular care committees for national organizations, including the American Heart Association and the American College of Cardiology.
