Patients between 40 and 75 years old with coronary artery disease caused by atherosclerosis may be eligible for this study. Candidates will be screened with a medical history, cardiovascular (heart and blood vessel) examination, electrocardiogram and blood tests. Those enrolled will be randomly assigned to take either an ACE inhibitor pill or a placebo (look-alike pill with no medicine) once a day for 3 months. No pills will be taken for the next month, and then participants will take the alternate pill for the next 3 months. That is, those who took ACE inhibitor for the first 3-month period will take placebo for the second 3-month period and vice versa. Blood pressures will be taken at the NIH Clinical Center or by the patient's physician at the end of the first and second weeks of the study. At the end of 3 weeks, patients will return to the Clinical Center for a blood draw of 6 cc (1/2 teaspoon) to assess kidney function. In addition, at the end of each 3-month study period, patients will undergo the following procedures at the Clinical Center: