A variation in the origin of the posterior descending coronary artery.

A rare congenital variation in the origin of the posterior descending artery (PDA) is described. The PDA arose from a vascular ring formed by a normally occurring communication between the right coronary artery and the left circumflex artery within the atrioventricular groove, then traversed the inferior septum following a normal branching pattern. No significant coronary artery stenoses nor abnormalities in the physiological data were present, thus ruling out the possibility of the communication being a collateral vessel secondary to ischemia. Our patient's uncommon communication represents only the third reported case of such an occurrence.