The secondary goal of this proposal is to evaluate in humans the relationship between coronary atherosclerosis (plaque buildup in the arteries of the heart) and wall shear stress (the force generated against the wall of the artery by the flow of blood). The reason for this sub-study is that there is great interest in understanding the characteristics that cause the progression of coronary atherosclerosis. Local forces such as shear stress may play an important role in the focal progression of "vulnerable" atherosclerotic plaques. Indeed, low shear stress is known to be an important factor in the early formation of atherosclerosis. However, the relationship of low shear stress to development and progression of advanced "rupture prone" ("vulnerable") plaques has not been elucidated. Our hypotheses are: (1) "Vulnerable plaques" are more commonly located at areas of low shear stress(2) "Vulnerable plaques" at areas of low shear stress are more likely to progress over the following 6 months than plaques located in normal shear stress regions.