Angina literally means "choking pain," and angina pectoris refers to a painful or uncomfortable sensation in the chest that occurs when part of the heart does not receive enough oxygen due to disease in the coronary arteries that supply blood to the heart.

The coronary arteries supply the heart muscle with oxygen and nutrients. The word "coronary" means a crown, and is the name given to the arteries that circle the heart like a crown.

Coronary artery disease (CAD) is the most common form of heart disease.   Coronary heart disease develops when one or more of the coronary arteries that supply the blood to the heart become narrower than they used to be, due to the buildup of cholesterol and other substances in the wall of the artery, affecting the blood flow to the heart muscle. Without an adequate blood supply, heart muscle tissue can be damaged.

Deposits of cholesterol and other fat-like substances can build up in the inner lining of these blood vessels and become coated with scar tissue, forming a cholesterol-rich bump in the blood vessel wall known as plaque. Plaque buildup narrows and hardens the blood vessel, a process called atherosclerosis, or hardening of the arteries.

Eventually these plaque deposits can build up to significantly reduce or block blood flow to the heart. A person may experience chest pain or discomfort from inadequate blood flow to the heart, especially during exercise when the heart needs more oxygen.

Angina is the body's warning sign that the heart is being overworked. It can be experienced in a variety of ways.

• Angina usually manifests as a feeling of pain, pressure, or tightness in the middle chest, especially behind the sternum (breastbone).
• The sensation may spread to the left shoulder, arm, and hand, or to the neck, throat, and jaw.
• The attack typically lasts for only a few minutes

It is very important to distinguish between two types of angina: stable angina and unstable angina. Both types result from problems within the coronary arteries.

• Stable angina results from a fixed obstruction of blood flow to the heart. It occurs when there is not enough blood for a fast-pumping heart, but sufficient blood can get through when the heart slows down and the individual is at rest. Stable angina typically is caused by widespread, irregular disease throughout the coronary arteries. The blockages that result may not seriously hinder the flow of blood, and they usually do not damage the heart unless a plaque (atheroma; fatty deposit within a blood vessel) suddenly ruptures.
• Unstable angina is due to a sudden interruption of blood flow to the heart due to a partial or complete blockage of the artery. Unstable angina comes on when a person is resting, asleep, or undergoes physical exertion (unlike stable angina, which usually comes on with a physical exertion). Symptoms of moderate or severe discomfort suddenly may develop in a person who has never experienced angina before, and attacks may become more frequent or increase in intensity.

Unstable angina can be dangerous, while stable angina generally is less serious. In order to identify which condition is present, a physician looks at when the angina pain occurs:

• Stable angina usually occurs during physical exertion or emotional stress or excitement. Stable angina doesn't lead to a heart attack in most people.
• Unstable angina can occur during rest, can awaken a person from sleep, and can appear suddenly during physical exertion. Unstable angina may quickly progress to a heart attack.

Unstable angina is a much more serious condition than stable angina because it may quickly progress to a heart attack. Some physicians regard unstable angina as a heart attack (until tests prove definitely that it is not a heart attack) because it is difficult to distinguish with early tests whether or not there has been damage to the heart muscle.

In unstable angina, cracks develop in the bulging plaque inside the coronary artery. These cracks, or partial ruptures of the plaque, are called plaque fissuring. It sets off an inflammatory reaction that dissolves the layer of tissue separating the plaque from the flowing blood. When the blood comes into direct contact with the plaque, it begins to form a clot around the damaged plaque.

Three things can happen:

• The clot gets bigger. Depending on how much of the artery it blocks, it will either cause the pain of angina or develop into a heart attack if it completely blocks the artery.
• The clot moves to another part of the artery and blocks it, causing a heart attack.
• The clot may simply be washed away after the crack in the plaque has healed.

What was previously a reasonably "stable" narrowing of the coronary artery has become "unstable," reducing the blood flow through the affected coronary artery and causing symptoms even at rest.

Unstable Angina Facts :

• The plaques that develop the crack, or rupture, are usually not the same ones that cause the critical narrowing of the coronary arteries.
• We do not know why a plaque suddenly ruptures.
• Because the clot that forms is formed by platelets, the treatment initially is to give antiplatelet treatments. This is a very different treatment from the "clot-busters" given for a heart attack.
• Unstable angina is considered as part of a spectrum called "acute coronary syndrome," which includes unstable angina and heart attack (known as myocardial infarction, either q-wave or non-q-wave types). What these conditions have in common is that symptoms result from rupture or erosion of a clot with obstruction of the coronary artery.
• A heart attack (known as a q-wave myocardial infarction) generally results from a more extensive rupture of a plaque, in which the whole clotting system, not just platelets, becomes involved. The treatment then uses "clot-busters" (called thrombolytics), which are very different drugs from antiplatelet drugs used for unstable angina.

It is vitally important for the doctor to make the distinction between stable angina, unstable angina, and a heart attack. This cannot always be done immediately.

Because the sensation of angina is alarming, many people believe they are having a heart attack the first time they experience it. But stable angina is NOT a heart attack. In fact, most people with stable angina respond well to modern treatments and live full lives for many years - if they follow their physician's advice, take medication as prescribed, and learn to look after their hearts.