Our methods of myocardial protection are demonstrated in 846 patients subjected to open heart surgery for correction of congenital heart disease. They include body hypothermia and injection cardioplegia using magnesium-asparate-procaine. The spectrum of myocardial protection reaches from normothermia without cardioplegic arrest during short periods of extracorporeal circulation to profound body hypothermia with multiple injections of the cardioplegic solution in complex cardiac malformations. The results in 586 patients with left to right shunt, 140 patients with cyanotic cardiac malformations and 120 patients with congenital valve lesions are presented. Attention is directed to possible negative sequelae of overdosage of magnesium-asparate.