J. Comp. Path. 2006, Vol. 134, 290^296 Anomalous Origin of the Left Coronary Artery from the Right Side of the Aortic Valve in Syrian Hamsters (Mesocricetus auratus) A. C. Dura ´n, T. Ferna´ndez-Gallego, B. Ferna ´ndez, M. C. Ferna´ndez, J.M.Arque´ à and V. Sans-Coma Department of Animal Biology, Faculty of Science, University of Ma Ł laga, E-29071 Ma Ł laga, and à University Hospital Carlos Haya, E-29011 Ma Ł laga, Spain Summary This study describes the coronary artery distribution patterns associated with the anomalous origin of the left coronary artery from the right side of the aortic valve in Syrian hamsters. The hearts of 15 a¡ected animals were examined by means of a corrosion-cast technique, histology and scanning electron microscopy.The hamsters be- longed to a laboratory inbred colony with a high incidence of coronary artery anomalies and bicuspid aortic valves.The aortic valve was tricuspid in eight hamsters and bicuspid in the other seven. In all cases, the right coronary artery was normal, whereas the left main coronary artery trunk arose from the right aortic sinus or from the right side of the ventral aortic sinus when the aortic valve was bicuspid. In 12 specimens, the left main trunk crossed the infundibular septum and then divided into the left circum£ex branch and the obtuse marginal branch. In another specimen, the course of the left main trunk was ventral to the right ventricular out£ow tract; in the remaining two, it surrounded the aorta dorsally. In man, some of these distribution patterns may cause myocar- dial ischaemia and sudden death. The present ¢ndings prove that the origin of the left coronary artery from the right aortic sinus occurs in primitive mammals such as the Syrian hamster, suggesting that the defect may occur in other mammalian species. Its possible occurrence should be borne in mind in domestic animals, especially in those with signs of myocardial ischaemia after strenuous activity. r 2006 Elsevier Ltd. All rights reserved. Keywords: coronary artery anomaly; heart; Syrian hamster Introduction In man, the origin of the left coronary artery from the right aortic sinus is the most common non-athero- sclerotic coronary artery disease associated with the risk of sudden death (Virmani et al ., 2001 ; Basso et al ., 2002 ). The anomaly is characterized by a normal right coronary artery and an aberrant left coronary artery, both arising from the right aortic sinus, either from two separate ostia or from two adjacent ostia conver- ging in a single ori¢ce (Petit and Reig, 1993 ). Autopsy and angiography surveys have indicated incidences of this defect as 0 Á 02% and 0 Á 05^0 Á 19%, respectively (see Petit and Reig [1993] for a review). To the best of our knowledge, the anomalous origin of the left coronary artery from the right aortic sinus has been reported only once in non-human mammals, namely, in a horse, unable to rise after castration and subjected to euthanasia after ine¡ective clinical treat- ment (Karlstam et al .,1999 ). In an investigation, still in progress, of coronary ar- tery anomalies in Syrian hamsters,15 hearts were found to have a left coronary artery arising from the right side of the aortic valve.The aims of the present study were (1) to describe the coronary artery distribution patterns of these specimens, taking into account the condition of the aortic root, the location of the coronaria ostia, and the course of the main coronary arterial branches, and www.elsevier.com/locate/jcpa ARTICLE IN PRESS 0021-9975/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi: 10.1016/j.jcpa.2005.11.005