Recently continuous warm blood cardioplegia (BCP) has been reported as a superior method of myocardial protection, but it is unknown which is more effective antegrade or retrograde cardioplegia. This study was performed to investigate the efficacy of antegrade infusion via aortic root and retrograde infusion via coronary sinus with continuous warm BCP in regard to metabolism, oxygen extraction ratio, serum enzyme release, cardiac function, and myocardial edema. Fourteen adult mongrel dogs were subjected to total cardiopulmonary bypass and cross-clamp of the aorta for 120 minutes, and followed by 60 minutes reperfusion. The dogs were divided into two groups according to the infusion type of continuous warm blood cardioplegia: Group A, antegrade warm BCP, and Group R, retrograde warm BCP. Changes in excess lactate (delta XL), redox potential (delta Eh), and myocardial lactate extraction ratio showed that aerobic metabolism could be maintained in group A and could not in group R. Myocardial oxygen extraction ratio during aortic cross-clamp was same in group A and in group R, but at 5 minutes after reperfusion it was significantly higher in group A than in group R (41 +/- 8% V.S. 22 +/- 9%). The incidence of ventricular fibrillation (V.F.) after reperfusion was significantly lower in group A than in group R (1/7 V.S. 7/7). CPK-MB and HBDH releases during aortic cross-clamp and 60 minutes reperfusion were lower in group A than in group R, but not significant. Generations of lipid peroxides (A-Cs difference) were lower in group R than in group A, but not significant.(ABSTRACT TRUNCATED AT 250 WORDS)