Congenital cardiac malformation with three-chambered right atrium and a persistent left cranial vena cava in a dog.

This report describes an unusual congenital abnormality in a dog in which multiple distinct membranes were observed within the right atrium, creating obstruction to venous return from both the cranial vena cava and the caudal vena cava. A persistent left cranial vena cava was also identified. In addition to a membrane in the typical location for cor triatriatum dexter, the dog also had a perforated membrane separating the main right atrial body and tricuspid valve from a more cranial right atrial chamber and the right cranial vena cava. Balloon dilation was performed successfully to alleviate the obstruction to systemic venous return created by the two membranes. Due to the unusual anatomic features, angiography plus echocardiography was useful to completely characterize the congenital abnormality prior to intervention.