We report a case of acute myocardial infarction and syncope in an 18-year-old athlete during high-performance exercise. A coronary arteriography and an angiographic computed tomography scan subsequently revealed a left coronary arterial origin from the right aortic sinus along with an intramural course of the left main stem. The patient was successfully treated with surgical unroofing of the left main stem from inside the aorta. To our knowledge, this is the first report demonstrating this type of anomaly pre- and postoperatively by use of angiographic computed tomography scan in the context of acute coronary syndrome.