Endocardial ossifying myxoma of the right atrium in a cat.

Primary cardiac neoplasms are rare in humans and animals. In humans, the most common primary cardiac tumor is the myxoma, which is frequently found in the left atrium. Cardiac myxoma has been reported in the dog but not in the cat. We describe the gross, immunohistochemical, and light microscopic examination of a myxoma in the right atrium of a 6-year-old domestic shorthair cat. Histologically, the tumor consisted predominantly of mesenchymal cells with several foci of bone and cartilage present. The tumor was encapsulated and benign.