A seven-year-old domestic shorthair (DSH) cat was presented with anorexia and dyspnea. Pleural-pericardial effusion was detected with thoracic radiographs and echocardiography. Echocardiography demonstrated a large, soft-tissue mass in the right ventricular wall, protruding both into the pericardial space and into the right ventricle. Postmortem examination findings included a large mass in the right ventricular wall and multiple smaller masses on the external surface of the left ventricle and on the internal surface of the pericardium. Results of the histopathological and immunohistochemical examinations of the masses were consistent with rhabdomyosarcoma. This is the first reported case of primary cardiac rhabdomyosarcoma in the cat.