A 35-year-old woman with angina of five years duration underwent elective cardiac catheterization and coronary angiography which revealed left main stenosis. Immediately afterwards, the patient became distressed, hypotensive and bradycardic. She died despite emergency percutaneous transluminal coronary angioplasty and resuscitative efforts. Autopsy confirmed isolated left coronary ostial stenosis due to the combination of a congenital abnormality of the ostium and initial segment of left main coronary artery, together with a superimposed myointimal flap bridging the ostium. A unique association was an abnormal configuration of the ostia of the branches of the aortic arch.