The coronary angiogram from this patient is depicted here. It revealed a 90% stenosis of the first diagonal branch of the circumflex coronary artery and lesser degrees of stenosis at multiple locations throughout the coronary vasculature. The electrocardiographic changes shown on the preceding pages are characteristic of reversible non-transmural myocardial ischemia caused by the failure of the coronary circulation to meet the metabolic demands of the myocardium, These changes usually occur during stress or exercise in patients with subtotal stenosis of one or more coronary arteries.