[Myocardial protection of temperature].
The effects of myocardial temperature on 120-minute preserved hearts were studied on heterotopically transplanted hearts of rats of isogeneic strain. Rats were divided in the following groups; the control group, the 0 degree C preservation group, the 5 degrees C group, the 10 degrees C group, the 15 degrees C group and the 20 degrees C group. Experiments were divided into the acute stage experiments and chronic stage experiments. The former included electron microscopic studies of the myocardium of heart transplants and serum enzymes of recipients. In the chronic stage experiments, the percentage of fibrosis was compared as an index of success. No hearts of the 20 degrees C group resuscitated, and by the indices of acute stage experiments, the 10 degrees C group and the 15 degrees C group showed considerable impairment; other groups showed less damage of the same degree. The chronic stage experiments indicated that the 0 degree C group was best, followed by the 5 degrees C group in the increasing order of temperature, evaluated by the rate of fibrosis. It may be concluded that hypothermia close to the freezing point has the best protective effects on the myocardium. Cold injury, even if present, may be transient and not harmful when ischemia is about 120 minutes. Comprehensive evaluation of various factors contributing isograft survival should include not only various methods examined in the acute stage but also an over-all evaluation of fibrosis in the chronic stage, since the myocardium of the graft shows a variability of findings in the acute stage.