A 23-year-old male referred for evaluation of a "choking" sensation with exertion and a murmur. A transthoracic echocardiogram demonstrated right atrial and ventricular dilatation, right ventricular volume overload, and a large secundum atrial septal defect (ASD) with left to right shunt and a calculated pulmonary-to-systemic blood flow ratio (Qp/Qs) estimated at 2.3 to 1. Cardiac catheterization also demonstrated evidence of the ASD with Qp/Qs of 4.6 to 1 with a significant step-up in oxygen saturation at the right atrial level. Additionally, an anomalous left main coronary artery (ALMCA) origin from the anterior right coronary cusp was suspected. Using 64-slice multidetector computed tomography coronary angiography (CCTA) the left main coronary artery was seen to arise from the right coronary cusp then traverse between the pulmonary trunk and the proximal ascending aorta before bifurcating into the left anterior descending and circumflex arteries that followed their normal courses distally. Based on the high risk nature of associated sudden death from an anomalous left main coronary artery (ALMCA) coursing between the aorta and the pulmonary trunk, the patient underwent surgical re-implantation of the ALMCA to the left coronary cusp and repair of the ASD. This case highlights a rare finding of a hazardous ALMCA in a patient with a secundum ASD and the utility of CCTA in evaluating the course of coronary anomalies along with other cardiac pathology.