Congenital single coronary artery is commonly associated with complex congenital heart diseases and manifests in infancy or childhood. But isolated single coronary artery is a rare congenital anomaly which can present as acute coronary syndrome in adults. The aim of the work is to discuss on isolated single coronary artery in two adults presenting as acute coronary syndrome. The first case underwent coronary angiography (CAG) through right radial route, but switched over to femoral for confirmation of diagnosis and due to radial spasm. An aortic root angiogram was done to rule out presence of any other coronary ostia. It revealed a single coronary artery originating from right sinus of valsalva. After giving rise to posterior descending artery branch at crux, it continued in the atrioventricular groove to the anterior basal surface of the heart and traversed as anterior descending artery. There was no atheromatous occlusive stenosis. This is R-I type single coronary artery as per Lipton classification. In the second case, angiography was completed through right radial route. It revealed a single coronary artery arising from right aortic sinus. Anterior descending and circumflex branch were originating from proximal common trunk of the single coronary artery and supplying the left side of the heart. The right coronary artery has diffuse atheromatous disease without significant stenosis in any major branch. This is R-III C type as per Lipton classification. A coronary anomaly of both origin and course is very rare. It may be encountered in adults evaluated for atherosclerotic coronary heart disease. Knowledge and understanding of anatomical types of this congenital anomaly will reduce time, anxiety, complications during CAG and cardiac surgery.