The abnormal formation of the circumflex artery from the right anterior sinus of Valsalva is generally considered benign and without any particular ischemic risk. Two cases are reported of myocardial ischemia in the region of the abnormal artery. In both cases an unstable angina was associated with objective criteria (electrocardiographic and isotopic) of myocardial ischemia. In one case the circumflex artery presented marked proximal stenosis compatible with the development of accelerated atherosclerosis. In the other case the circumflex artery was free of any stenosis and the ischemic manifestations observed seem to be due to the abnormal origin of the vessel only. Certain cases of the circumflex artery anomaly can, therefore, be complicated by myocardial ischemia, and the benign nature of the anomaly needs to be re-examined.