Among patients with stable ischemic heart disease who are referred for coronary angiography, a substantial proportion have non-obstructive coronary artery disease (CAD). Ischemia based on symptoms or stress testing may be due to coronary microvascular dysfunction in up to 40% of these patients. However, the mechanisms and optimal treatment of coronary microvascular dysfunction are unknown. Aberrant platelet activity and inflammation have been hypothesized as mechanisms of microvascular dysfunction. Investigators plan to evaluate association between platelet activity, inflammation, and coronary microvascular dysfunction in stable women referred for coronary angiography, and to identify non-invasive correlates of coronary microvascular dysfunction in these patients.