Coronary artery disease, also called coronary heart disease, or simply, heart disease, is the No. 1 killer in America, affecting more than 13 million Americans.

What Is Coronary Artery Disease?

Coronary artery disease is atherosclerosis of the coronary arteries, producing blockages in the vessels which nourish the heart itself. Atherosclerosis occurs when the arteries become clogged and narrowed, restricting blood flow. Without adequate blood flow from the coronary arteries, the heart becomes starved of oxygen and vital nutrients it needs to work properly.

How Does Coronary Artery Disease Develop?

Your coronary arteries are blood vessels on the heart. They are smooth and elastic, allowing blood to flow freely.

Before your teen years, fat can start to deposit in the blood vessel walls. As you get older, the fat builds up. This causes injury to your blood vessel walls. In an attempt to heal itself, the fatty tissues release chemicals that promote the process of healing but make the inner walls of the blood vessel sticky.

Then, other substances, such as inflammatory cells, proteins, and calcium that travel in your bloodstream start sticking to the inside of the vessel walls. The fat and other substances combine to form a material called plaque, which can narrow the flow of blood in the artery (atherosclerosis).

Some plaque deposits are hard on the outside and soft and mushy on the inside. Some plaque is fragile, cracking or tearing, exposing the soft, fatty inside. When this happens, platelets (disc-shaped particles in the blood that aid clotting) come to the area, and blood clots accumulate on the injured vessel wall. This causes the artery to narrow even more. Sometimes, the blood clot breaks apart by itself, and blood supply is restored.

Over time, the inside of the arteries develop plaques of different sizes.

Eventually, a narrowed coronary artery may develop new blood vessels that go around the blockage to get blood to the heart. However, during times of increased exertion or stress, the new arteries may not be able to supply enough oxygen-rich blood to the heart muscle.

In other cases, the blood clot may totally block the blood supply to the heart muscle, causing what is called an acute coronary syndrome. This is actually a name given to three serious conditions:

Unstable angina: chest pain that can often be relieved with oral medications, is unstable, and may progress to a heart attack. Usually more intense medical treatment or a procedure is required to treat this acute coronary syndrome.
Non-ST segment elevation myocardial infarction (NSTEMI) or "non-Q-wave MI": This heart attack, or MI, does not cause typical changes on an electrocardiogram (ECG). However, chemical markers in the blood indicate that damage has occurred to the heart muscle.
ST segment elevation myocardial infarction (STEMI) or "Q-wave MI": This heart attack, or MI, is caused by a prolonged period of blocked blood supply. It affects a large area of the heart muscle, and causes changes on the ECG as well as chemical markers in the blood.

Some people have symptoms that tell them that they may soon develop an acute coronary syndrome, others may have no symptoms until something happens, and still others have no symptoms of the acute coronary syndrome at all.

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