The condition of coronary arteries and aortic valves was studied in 552 Syrian hamsters belonging to a single family subjected to high endogamous pressure. The study was carried out using a corrosion-cast technique. In 178 hamsters the aortic valve was bicuspid. In 138 specimens, 54 of them with normal aortic valves and 84 with bicuspid aortic valves, anomalies in the origin of the coronary arteries could be classified in three morphologic types: left coronary artery from the pulmonary trunk (36 cases); single right coronary artery (84 cases); left coronary artery from the dorsal aortic sinus (18 cases). Results of a chi 2 contingency test show that the frequency of left coronary artery from the pulmonary trunk and single right coronary artery significantly increases when the aortic valve is bicuspid. The present findings suggest that there is a developmental complex consisting of biscuspid aortic valve and anomalous origin of the coronary arteries.