Atherosclerosis of the coronary arteries is a disease that can begin at a young age, progressing over time to the point where it can cause problems such as angina and heart attack. Fatty and cholesterol deposits form in the wall of the blood vessel and progress with time, eventually causing a narrowing of the blood vessel and decreasing blood flow. Theses deposits are called plaque. Plaques vary in multiple characteristics including severity, the amount of calcium, and whether they are soft and “mushy” with a firm, thin “cap” (often considered “unstable” because they may be more likely to rupture) or more organized and “firm” (often considered “stable” only because they may be less likely to rupture). When and which plaques cause heart attacks is not fully understood but it is generally felt that heart attacks are more likely to be caused by unstable plaques that rupture and cause blood clot formation. Severe narrowing from plaques, whether soft or firm, may cause many symptoms, including angina, by severely decreasing oxygen rich blood flow to the heart muscle.