From epidemiological and experimental evidence it has been concluded that ovarian steroids have a large variety of cardiovascular effects. Among these are a direct action on the vascular wall, alterations in hemodynamics, modification of protein metabolism involved in the arteriosclerosis process, and alterations in the risk of cardiovascular morbidity and mortality. Some of the earlier epidemiological studies indicated an increased risk of cardiovascular disease (CVD) in estrogen users, but later on the majority of the published studies reported consistently a striking decrease in CVD by about 50%. The consistency in the positive results observed in successive epidemiological reports from various countries strongly suggest a protective effect of hormone replacement therapy on CVD morbidity. However, the direct demonstration of a protective effect of estrogens on CVD morbidity and mortality can only be made by long-term prospective controlled studies.