This study will non-invasively investigate endothelial function in patients with cardiac risk factors and with established coronary artery disease. Patients will undergo testing of endothelial-mediated nitric oxide release in the brachial artery, using a recently developed,non- invasive ultrasound method. Brachial responses determined by this method were recently shown to closely correlate with nitric oxide-dependent vasodilation in the coronary circulation. The effects of interventions to reduce coronary risk factors on endothelial vasomotor functions will also be examined by completing studies in patients before and after initiation of lipid-lowering therapy smoking cessation, estrogen replacement therapy, intensive control of diabetes, and initiation of cardiac rehabilitation. The time course and extent of improvement will be examined by performing serial studies of endothelial vasomotor function using the non-invasive method.