Objective To observe the myocardial injury attributed to cardiopulmonary resuscitation, and to evaluate the impact of 4 ℃ saline perfusion on the ultra structure of myocardium. Method Twelve Pekimg white swine were induced to make models of ventricular fibrillation by direct current shock. Cardiopulmonary resuscitation was initiated 4 minutes after ventricular fibrillation established, and 10 swine survived from resuscitation. These swine were randomly(random number ) divided into hypothermia group ( n = 5) ( 4 ℃ saline infusion to lower the temperature) and control group ( n = 5). Haemodynamics were monitored. And ultra structure of myocardium was observed under electron microscope 24 hours later. The Mann-Whitney test was used to compare the consecutive variables of 2 samples. Results The damage to the ultra structure of myocardium, myofilaments and mitochondria, was found in the control group, while that to a much lesser extent in the hypothermia group was observed. Conclusions After cardiopulmonary resuscitation, 4 ℃ saline infusion has a protective effect on myocardium.