Collateral coronary circulation in the absence of obstructive coronary artery disease.

The presence of collateral coronary circulation almost always accounts for significant obstructive coronary artery disease and its development remains unclear. We present two cases wherein there was a large collateral artery in a patient with angiographically normal coronary arteries. In both cases, the vessel ran in the atrioventricular groove, between the distal right coronary artery and the circumflex artery. We believe that this vessel is of congenital origin and after reviewing the literature we describe the angiographic features that distinguish such a vessel from collaterals that are secondary to coronary stenosis or hypoxia.