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Background: In older postmenopausal women, high levels of endogenous estrogen have been related to adverse health outcomes including ischemic arterial disease (IAD). Whether estrogen receptor-α (ESR1) and -β (ESR2) polymorphisms modulate the effects of estrogens on IAD has not been investigated., Methods: In the Three-City prospective cohort study among subjects older than 65 years, we used a case-cohort design in which plasma levels of total and bioavailable 17β-estradiol were measured. After exclusion of postmenopausal women using hormone therapy, a random subcohort of 533 women and 105 incident cases of first IAD events over 4 years of follow-up were analyzed. Five common polymorphisms of ESR1 and ESR2 were genotyped. Hazard ratios (HRs) of IAD for a 1-SD increase in hormones levels by the genotypes were estimated from Cox models after adjustment for cardiovascular risk factors and a correction for multiple testing. We also investigated the role of hemostasis and inflammation as potential mediators., Results: Neither estrogens nor IAD risk was significantly associated with estrogen receptor polymorphisms. Overall, IAD risk increased with total estradiol [HR1.40, 95% confidence interval (CI) 1.11-1.77]. Stratified analysis by genotypes showed that total estradiol was positively related to IAD risk in women with ESR1 rs9340799-AA genotype but not in women with the AG/GG genotype (HR 1.62, 95% CI 1.22-2.17 and HR 1.03, 95% CI 0.81-1.30, respectively; P for interaction <.05). An additional adjustment for hemostatic variables reduced the HR by about one third in women carrying the rs9340799-AA genotype (HR 1.41, 95% CI 1.06-1.90)., Conclusion: The ESR1 rs9340799 genotype may modify the IAD risk related to high endogenous estrogens levels in older postmenopausal women. Hypercoagulability may act as a mediator.