A 11-year-old castrated male cat was referred for cranial mediastinal mass. A diagnosis of thymoma was made after various examinations, and the cat underwent thymectomy. Approximately 1 hour after anesthesia recovery, a sudden intrathoracic hemorrhage was observed and the cat collapsed. During an urgent revision surgery to achieve hemostasis, the cat underwent cardiopulmonary arrest due to hypovolemic shock. Return of spontaneous circulation was achieved after direct cardiac massage; however, severe hypovolemia continued requiring immediate blood transfusion. Due to lack of availability of feline blood product, xenotransfusion of stored canine packed red blood cells was performed as emergency treatment, which successfully stabilized the cat’s hemodynamic status. An additional transfusion of fresh feline whole blood was performed. A transient delayed hemolysis was observed 5 days after the xenotransfusion, and no other adverse event occurred. Xenotransfusion of canine packed red blood cells was considered an acceptable alternative to allotransfusion in emergency case of acute hemorrhagic event in cats.