We present a case of a rare congenital cardiac anomaly. Magnetic resonance imaging accurately demonstrated a left circumflex aortic arch. This finding was not apparent on a prior conventional angiogram or echocardiography. Magnetic resonance imaging documentation of this anomaly is uncommon. Review of the embryonic development, clinical presentation of complete and incomplete vascular rings, and additional associated cardiac anomalies are discussed. This is one of only a few reported cases of a left circumflex aortic arch.