An 82 year old man who was previously well was admitted to hospital with a five day history of unstable angina. His admission ECG was normal but subsequent ECGs showed T wave inversion in anterior leads. The peaked creatine kinase concentration was 555 u/l. Despite medical treatment he had recurrent chest pain that was associated with dynamic inferolateral ST depression. Therefore, coronary angiography was performed. The left coronary artery could not be cannulated in the usual position. The right coronary artery was super dominant with an anomalous left coronary system arising at the ostium of the right coronary artery. The sole coronary stenosis was in the mid segment of the anomalous left main stem. Left ventricular function was preserved. He has been free of chest pain since his coronary artery bypass surgery.