More than 30 epidemiological studies of the association between CHD and ERT/HRT in postmenopausal women have been reported. These studies have consistently shown a reduction in the incidence of CHD62,63 and in the overall mortality64 of postmenopausal women using ERT/HRT.65- 69 In an early report on the Nurses' Health Study70 cohort, for example, more than 32,000 postmenopausal women who were initially free of CHD were followed up at 2 and 4 years. Women who were currently using ERT had a relative risk (RR) of 0.30 (95% confidence interval [CI], 0.14-0.64; P = .002) for a nonfatal myocardial infarction (MI) and fatal CHD compared with women who had never used ERT. Ever users, that is, women who had used ERT in the past but who were not current users, had an RR of 0.59 (95% CI, 0.33-1.06), although this was not statistically significant (P = .08). The type of ERT most frequently used by the participants was unopposed oral CEE; very few women used HRT. In a 16-year follow-up of the Nurses' Health Study cohort, Grodstein et al71 reported similar beneficial effects. Among current users of ERT, the multivariate-adjusted RR for major CHD was 0.60 (95% CI, 0.43-0.83); for postmenopausal women who were currently using HRT, the adjusted RR was 0.39 (95% CI, 0.19-0.78). A similar beneficial effect of ERT/HRT use on CHD death was observed for the 41,837 participants in the Iowa Women's Health Study.69 The RR of CHD death with ERT/HRT use was reduced in women with (RR, 0.56; 95% CI, 0.30-1.04) or without (RR, 0.71; 95% CI, 0.57-0.89) a family history of breast cancer. In a Swedish cohort study, Falkeborn et al72 observed 23,174 postmenopausal women for an average of 5.8 years. They reported that in women who were younger than 60 years old at the onset of the study, oral CEE or estradiol reduced the incidence of a first MI by 31% compared with never users (RR, 0.69; 95% CI, 0.54-0.86). Estradiol combined with levonorgestrel also resulted in a reduction in risk for a first MI (RR, 0.53; 95% CI, 0.30-0.87). The cardioprotective effect did not extend to women prescribed estriol compounds. Other studies64,67,73 have supported a cardioprotective role for ERT/HRT. Meta-analyses of these studies5,74 suggest that ERT reduces the risk of CHD by 35% to 50%; fewer studies74 have evaluated the cardioprotective effect of HRT, but these have likewise reported beneficial effects.