A 70-year-old man was scheduled to undergo corrective osteotomy under general anesthesia. During the operation, a fluid warmer was applied, with his body temperature assessed with the use of an axillary temperature probe. Near the end of the operation the pressure waveform from the radial artery and pulse oxymeter became flat. Palpation of the carotid artery revealed no heart rate, the electrocardiographic tracing continued to be sinus rhythm, and pulseless electrical activity was diagnosed. The infusion of cardiovascular drugs was also performed. However, the hemodynamic status of the patient deteriorated to severe hypotension, with atrial fibrillation, paroxysmal ventricular tachycardia. The patient was assessed as hypothermia from a rectal temperature of 30.5℃. After active warming methods for 1 hour the cardiovascular status of the patient became stabilized.