The effect of terminal warm blood cardioplegia (TWBC) was evaluated from the incidence of ventricular fibrillation and myocardial metabolism after release of aortic clamping in 70 patients (group I) who underwent open heart surgery using TWBC compared with 70 patients (group II) without TWBC. The incidence of ventricular fibrillation after unclamping in group I was 19.7% which was statistically less than 68.6% in group II. Both excess lactate (delta XL) and redox potential (delta Eh) demonstrated that anearobic myocardial metabolism after reperfusion was restored more rapidly in group I than in group II. Multivariate analysis showed the incidence of ventricular fibrillation after reperfusion was related to high concentrations of both calcium and sodium and low concentration of potassium in reperfused blood in group II. But it was only related to left ventricular myocardial temperature in group I. High concentration of calcium and low concentration of potassium in reperfused blood, and low myocardial temperature were most related to anearobic metabolism of myocardium following reperfusion in group II, whereas only pH value was closely related to recovery for myocardial metabolism in group I. In conclusion, TWBC was useful for improving microcirculation in myocardium and avoiding calcium-overload to myocardial cells, and resulted in reducing reperfusion injury in myocardium. Furthermore, acid content of TWBC and enough amount to raise myocardial temperature would provide more efficacy on myocardial preservation.