Angina refers to the symptoms a patient experiences any time the heart muscle is not getting enough blood flow through the coronary arteries. Stable angina is angina that occurs in a nearly predictable fashion, that is, with exertion or after a big meal. Stable angina generally indicates that a stable atherosclerotic plaque is present in one of the coronary arteries, causing a partial obstruction of that artery. When the patient is at rest, the partially obstructed artery is able to meet the needs of the cardiac muscle. Thus, stable angina implies a fixed, stable atherosclerotic plaque.
Unstable angina is angina that occurs sporadically, or unpredicatably, or at rest.
There is no particular pattern to unstable angina. Unstable angina implies the existence of an unstable plaque, one that has partially ruptured, or in which blood clots may be forming and breaking off, so that the lumen of the artery is not fixed, but is changing. Patients with unstable angina have a high incidence of total occlusion of the coronary artery, and thus a high incidence of heart attacks. A myocardial infarction , or heart attack, occurs when a coronary artery becomes completely occluded, so that the heart muscle supplied by that artery dies. A heart attack, therefore, is death of heart muscle.