Aim I: To determine the activity of the endogenous endothelin system in the coronary circulation in humans with coronary endothelial dysfunction and atherosclerosis risk factors. Aim II: To assess the potential of chronic endothelin receptor antagonists to improve preexisting coronary endothelial dysfunction and myocardial perfusion in humans and Aim III: To assess the effect of chronic endothelin receptor antagonism on the endogenous nitric oxide system in association with oxidative stress in humans with early coronary disease risk factors.