Operations on the open heart under perfusionless deep hypothermia were performed in 3,141 patients with congenital cardiac defects. The patients ages ranged from 3 months to 44 years. The body was cooled to 26-24 degrees C by covering with crushed ice. Cooling was performed under conditions of not deep ether anesthesia with the use of minimum doses of narcotic analgetics (morphine 0.5 mg/kg). Lactacidemia was registered during hypothermia. In contrast to lactate, the content of fatty acids and 11-hydroxycorticosteroids during all the stages of hypothermia did not change significantly. The time of circulatory arrest ranged from 10-89 min. It took 2-7 min to restore cardiac activity. Of 3,141 patients operated on, 265 died (8.44%). The mortality pattern demonstrated that the major cause of death was cardiac insufficiency (5.9%). Neurological sequelae were observed in 110 patients (3.5%). Based on the results of tests with Luria's neuropsychological method, neurological disturbances were registered in 15.4% of patients. The frequencies of neuropsychological complications were not related to the time of circulatory arrest. Unstable hemodynamics after operation was the most contributory factor to the development of neurological complications. Perfusionless deep hypothermia is an efficient method providing conditions for performance of open heart operations, and it can be used in surgical repair of congenital cardiac defects.