Women suffer disproportionately than men from Cardiac Syndrome X ( chest pain in the absence of flow limiting coronary artery stenosis). Coronary microvascular disease is hypothesized to mediate chest pain in this syndrome. This disorder of the small heart vessels (arterioles) compared to the large vessels (arteries) is not diagnosed during routine heart catheterization. This results in delays in diagnosis, missed opportunities for treatment, and likely contributes to the increased death rate from coronary heart disease in women compared to men.