The primary goal of this project is to evaluate the effect of the cholesterol lowering drug Atorvastatin on the composition and character of coronary atherosclerosis (heart blockages). Atorvastatin is known to reduce cholesterol, reduce cardiac events, and halt the progression of coronary atherosclerosis. However, the reduction in cardiac events is out of proportion to the reductions in the total amount of atherosclerosis. Thus, the drug likely decreases cardiac events by changing the composition of the coronary atherosclerotic plaques. It is likely that the drug causes the "heart blockage" to change from a "vulnerable plaque" to a "stable" plaque. There are several features of "vulnerable plaques" that can be detected in arteries of the heart using intravascular ultrasound. The goal of this project is to examine the effects of atorvastatin on atherosclerosis plaque composition using this intravascular ultrasound in patients undergoing serial cardiac catheterizations. Our hypothesis is that atorvastatin will reduce the number of "vulnerable plaques" and increase the number of "stable plaques" seen by intravascular ultrasound. We plan to enroll a total of 20 patients. The patients will be evaluated by cardiac catheterization with intravascular ultrasound analysis and then be treated with atorvastatin for 6 months. These 20 patients will return to the cardiac catheterization laboratory 6 months later for a repeat catheterization with intravascular ultrasound evaluation.