Case Presentation. A 54-year-old male with a history of hyperlipidemia was referred to our institution for evaluation of chest pain. The patient developed chest discomfort in the setting of atrial fibrillation with a rapid ventricular response. Having spontaneously converted to sinus rhythm during an emergency department evaluation, the patient was referred to our clinic for further evaluation of his condition and associated symptoms. The patient elected to proceed directly to cardiac catheterization rather than undergo stress testing. Coronary angiography demonstrated an anomalous takeoff of the left main coronary artery from the ascending aorta. Coronary computed tomographic angiography (CTA) was performed in order to delineate the vessel’s course. CTA revealed that the left main originated posteriorly from the ascending aorta, coursing between the ascending aorta and the pulmonary artery. The incidence of abnormal aortic origin of the left main coronary artery is unclear, although literature suggests that it is an extremely rare coronary anomaly.