In this paper we discuss 2 unprecedented examples of coronary ostial atresia in adults. The first case documents a case of left main ostial agenesis with intercoronary communication through a retroaortic Kugel anastomotic collateral. The second case describes a right coronary artery (RCA) ostial agenesis with a preconal intercoronary anastomosis in association with supravalvular pulmonary stenosis. While atresia of the left coronary artery ostium is a rare anatomic variant of the coronary circulation, atresia of the right coronary ostium is exceedingly rare and not reported in adults (1). Correlative images of coronary computed tomography angiography (CTA) using a 64-slice multidetector computed tomography and coronary catheterization angiograms are presented for both cases, and the arterial collateral pathways between the proximal right and left coronary systems are discussed. We also reviewed the differences between congenital and developmental forms of abnormalities.