Abstract-Women younger than 75 years with stable angina or acute coronary syndrome have higher cardiac mortality than similarly aged men, despite less obstructive coronary artery disease. To determine whether the myocardial structure and coronary microvasculature of women differs from that of men, we performed histological analysis of biopsies from nonischemic left ventricular myocardium from 46 men and 11 women undergoing coronary artery bypass graft surgery who did not have previous cardiac surgery, myocardial infarction, heart failure, atrial fibrillation, or furosemide therapy. The 2 patient groups had similar clinical characteristics, apart from a lower body surface area (BSA) in women (Pϭ0.0015). Women had less interstitial fibrosis than men (Pϭ0.019) but similar perivascular fibrosis. Arteriolar wall area/circumference ratio, a measure of arteriolar wall thickness, was 47% greater in women than men (Pϭ0.012).Cardiomyocyte width and diffusion radius were positively correlated, and capillary length density was negatively correlated with BSA (PϽ0.05). Whereas cardiomyocyte width, capillary length density, diffusion radius, and cardiomyocyte width/BSA ratio were similar for men and women, women had a greater diffusion radius/BSA ratio (Pϭ0.0038) and a greater diffusion radius/cardiomyocyte width ratio (Pϭ0.027). Women also had lower vascular endothelial growth factor (VEGF) receptor-1 levels (Pϭ0.048) and VEGF receptor-1/VEGF-A ratio (Pϭ0.024) in plasma. We conclude that women with extensive coronary artery disease have greater arteriolar wall thickness and diffusion radius relative to BSA and to cardiomyocyte width than men, which may predispose to myocardial ischemia. Additional studies of larger numbers of women with less extensive coronary artery disease are required to confirm these findings. Key Words: gender Ⅲ ischemic heart disease Ⅲ myocardial fibrosis Ⅲ coronary microvasculature I schemic heart disease of women is different from that of men. 1,2 Women with stable angina referred for angiographic evaluation are less likely to have significant coronary artery disease, 3 yet women younger than 75 years with stable angina have a higher coronary standardized mortality ratio than men. 4 Moreover, when women present with an acute coronary syndrome, they are less likely to have an STsegment elevation myocardial infarction and more likely to have unstable angina, 5 and although they are less likely to have significant coronary artery disease, 3,5 women less than 75 years of age with myocardial infarction have a higher risk of coronary death than men. 3,6 -8 Evidence for a greater role for coronary microvascular dysfunction in ischemic heart disease of women is the report that retinal arterial narrowing, a marker of lower hyperemic myocardial blood flow and perfusion reserve, 9 predicted coronary events in women, but not in men. 10 To investigate the possibility that the different characteristics of ischemic heart disease in men and women reflect differences in myocardial structure and coronary microvascula...