Anomalous origin of the circumflex coronary artery is extremely rare and may cause serious perioperative myocardial injury associated with correction of coexisting congenital malformations. We describe a 15-year-old female patient who underwent surgical correction of an aortopulmonary window at 13 months. Fourteen years later, she presented with dyspnea on exertion associated with angina. On cardiac catheterization, she was noted to have a step-up in oxygen saturation in the pulmonary artery and retrograde filling of the circumflex coronary artery from the left anterior descending coronary artery, with drainage into the pulmonary artery. The patient underwent surgical bypass of the anomalous circumflex coronary artery and ligation of its anomalous origin in the pulmonary artery. Her postoperative course was uneventful, with complete relief of symptoms. We have reviewed this rare congenital anomaly and its therapeutic options.