Coronary arteriography is the only examination by which the diagnosis of single coronary artery may be made in vivo by demonstrating the presence of an entire coronary system arising from a common trunk. The discovery may be made under two distinct sets of circumstances: 1 degree Coronary ischaemia in a young subject. Arteriography confirms the diagnosis and the customary 2 degrees Coronary ischaemia in an older individual. Arteriography shows atherosclerotic lesions in a single coronary artery. The severity of the condition is related to the proximal character of the stenoses. The most logical therapeutic approach is aorto-coronary bypass if the quality of the distal network as seen at arteriography makes it possible.