The primary objective of this study is to test the hypothesis that myocardial perfusion heterogeneity, quantified by Markovian Homogeneity analysis of cardiac PET perfusion images, will improve in a quantitative manner after treatment with selective ETA receptor antagonist darusentan 100 mg per day for 2 weeks compared to baseline and post-treatment PET scans in clinically stable subjects with coronary atherosclerosis and/or risk factors.