Cardiac involvement secondary to mediastinal lymphoma in a cat: regression with chemotherapy.

Mediastinal lymphoma with neoplastic invasion into the heart was diagnosed in a 9-year-old castrated male domestic short hair cat. The neoplastic infiltrate was seen throughout the atria and atrial septum, surrounded the aortic root, and resulted in narrowing of the right ventricular outflow tract. Chemotherapy resulted in resolution of the echocardiographic abnormalities and the cat's clinical signs until the patient was euthanized 58 days later following development of neurologic signs. Mediastinal lymphoma with myocardial invasion and response to chemotherapy has not been documented previously in the veterinary literature.