Coronary atherosclerosis is a major cause of death in women in the United States. Although coronary artery bypass surgery decreases symptomatic and clinical evidence of ischemia, it does not alter the underlying process. Patients may present several years later with recurrent symptoms that may be a result of occlusion of saphenous vein grafts, development of atherosclerotic disease in vein grafts, or progression of underlying disease. Any intervention that can reduce the rate of progression of coronary atherosclerosis following bypass surgery would provide significant benefit for women following bypass surgery and possibly for other women with atherosclerotic disease. Observational studies suggest that postmenopausal estrogen replacement therapy is associated with a reduction in cardiac morbidity.