The clinical history of an adult patient with anginal-like pain is described. A coronary angiography revealed the existence of a hypoplastic left coronary artery, a right coronary artery which passed around the posterior surface of the heart and continued into the anterior surface of the heart to give off an anterior descending artery and the presence of a "conus" artery. The embryonic genesis of hypoplastic coronary artery and of a similar aberration, single coronary artery, are discussed.