Complete transposition of the great arteries with a patent ductus arteriosus, atrial septal defect, and juxta-arterial ventricular septal defect in a cat

An 11-week-old male intact Siamese cat was presented for evaluation of a grade V/VI parasternal systolic murmur. Echocardiography revealed multiple congenital cardiac abnormalities, including parallel orientation of the aorta and main pulmonary artery, a patent ductus arteriosus, and a juxta-arterial ventricular septal defect. Cardiac remodeling secondary to these congenital defects was also noted. The patient was clinically stable at the time of presentation, but the owner ultimately elected for humane euthanasia before the onset of cardiac decompensation. Postmortem necropsy was performed to confirm the congenital deformities identified on echocardiography. An ostium secundum atrial septal defect that was not originally detected on echocardiography was discovered at this time. The cat was diagnosed with a complete transposition of the great arteries and concurrent congenital defects that allowed for mixing of the pulmonary and systemic circulatory systems. This case report describes a congenital defect that is infrequently reported in veterinary medicine, as well as the utility of antemortem echocardiography and gross necropsy findings to characterize this deformity.