The efficacy and safety of very hot (65°C/149°F) intravenous fluid (IVF) were compared with those of conventional warm (38°C/100.4°F) IVF in the treatment of hypothermia. Eight anesthetized beagles (11–20 kg) were studied. Blood pressure (BP), pulse (P), and core temperature (cT°) were recorded at baseline, during hypothermia, and during rewarming. The plasma free hemoglobin (PFHg) was measured to assess hemolysis. Each subject was cooled to 32°C/89.6°F and assigned to receive either 65°C or 38°C IVF via a specially designed multiport balloon-tipped catheter in the superior vena cava (SVC). The IV fluid rate was 80% of the blood volume per hour. Conventional rewarming methods were used in all subjects. After 2 hours the subjects were killed and the SVC was examined for injury. The rate of rewarming was 2.9°C/hour in the 65°C IVF group and 1.25°C/hour in the 38°C IVF group. The cT° was significantly different in all subjects after 1 (35.2° ± 1.03°C vs. 33.2° ± 0.5°C; p < 0.006) and 2 (37.6° ± 1.17°C vs. 34.3° ± 0.9°C; p < 0.004) hours of rewarming. The BP, P, and PFHg were not different. Visual examination of the SVC revealed two lesions in the 65°C IVF group and one in the 38°C group. Mechanical or thermal injury could not be differentiated. We conclude that 65°C IVF is more effective than 38°C IVF in the treatment of hypothermia. In addition, 65°C IVF did not uniformly cause hemolysis or injure the SVC.