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. If you experience any symptoms in the checklist below, you should let your doctor know because they could be indications of heart disease.

These symptoms are not always caused by heart disease; they may be harmless or due to other medical conditions. But if you already have heart disease, these symptoms are enough to indicate a potential heart problem and reason enough for you to check with your doctor, especially if these symptoms are new.

• Discomfort in your chest - that comes on during physical exertion or emotional stress; it may spread to your arms, neck, lower jaw, face, back, or stomach. If this discomfort is from your heart, it is called angina.

• Unusual breathlessness - when doing light activity or when you are at rest can be a symptom of heart disease. Breathlessness that comes on suddenly may be an important warning

• Palpitation - is the term used to describe the condition in which you feel your heart beat faster or more forcefully than usual, or in an irregular pattern. Palpitations may be a symptom of heart disease, especially if they last for a few hours, if they come and go over several days, or if they cause chest pain, breathlessness, or dizziness.

• Fainting - (or the sensation that you are about to faint) can be caused by inadequate oxygen reaching the brain, which may be due to heart disease.

• Swelling - or fluid retention (also known as edema) is fluid buildup in your tissues. This usually happens around the ankles, legs, lungs, and abdomen. Swelling of the legs can be perfectly normal for some people after working many hours on their feet. However, it can also be a sign that the heart is not pumping efficiently.

• Fatigue - has many causes, but it’s worth seeing the doctor if you feel unusually tired, especially if it is combined with other suspicious symptoms noted above.

Sometimes, however, the danger signal from the heart is more dramatic. Atherosclerosis causes plaques to accumulate in the coronary arteries. These plaques are lumps and bumps within the coronary arteries that can contain cholesterol, white blood cells, and other substances.

Sometimes they grow to block the arteries and sometimes they are small and do not affect the blood flow. A cap forms on top of the plaque to keep the contents from seeping into the bloodstream. These plaques can be quiescent and not cause a problem.

Occasionally, however, the cap on a plaque can rupture (and this can happen on a big or small plaque), exposing its contents to the bloodstream. When this happens, the contents of the plaque are mixed with the blood and can cause formation of a blood clot.

If the blood clot blocks an important artery supplying blood to the heart, heart muscle can be suddenly deprived of vital oxygen and nutrients. At this point, every minute counts because heart muscle cannot survive long without receiving fresh blood.

Within a relatively short period the damage to the heart can be severe and permanent. This event is what doctors call a myocardial infarction. Everyone else calls it a heart attack. The symptoms of a heart attack are often similar to those of angina, but much worse and more persistent.

The classic description of a heart attack is a “crushing chest pain” that does not go away, even after resting or taking angina medication. Other symptoms, which sometimes can even occur without chest pain, can include sweating, nausea, light-headedness, and breathlessness.

These symptoms are often confused with those caused by other, much less serious conditions. Here’s the important thing to keep in mind: Don’t take chances. If you experience symptoms that may represent a heart attack, you should call an ambulance immediately and be brought to an emergency department; your survival may depend upon it.

It is natural to feel reluctant to ask for help, and for many people it is embarrassing to call an ambulance. Also, heart attacks often do not start like they do in the movies, with crushing pain that causes you to clutch your chest. Uncertainty is quite common, but you should not wait to see whether your condition gets worse.

This is the time to call 911. As a general rule, doctors recommend that angina-like discomfort that occurs without exertion or persists for more than ten minutes should be treated as a sign of a possible heart attack, even if more dramatic symptoms do not develop.

The National Heart, Lung, and Blood Institute of the National Institutes of Health recommends that people should not wait more than five minutes before calling 911. Why the rush? Treatment, particularly in the first hour, can make an enormous difference in improving a person’s chance of survival.

Unfortunately, most people experiencing a heart attack wait much longer to seek help. According to experts, most people wait two or more hours before obtaining medical attention.