The influence of intermittent warm blood cardioplegia (WBCP) on myocardial function and metabolism was studied. Fourty-two adult mongrel dogs were used. The isolated heart of one dog was perfused by the cross circulation method with another support dog. The dogs then were divided into three groups. In group I (n = 6), the empty beating heart was perfused with warm blood (WB) kept at 36 degrees C for 100 minutes. In group II (n = 7), the arrested heart was perfused with continuous WBCP using modified Fremes solution for 100 minutes. In group III (n = 8), the arrested heart was perfused with WBCP for 10 minutes following a 15-minute non-perfusion period. This perfusion method was repeated four times. The E max, LV developed pressure, +/- LV dp/dt and LVEDP were all measured to evaluated the myocardial function. In addition, the coronary venous blood pH, myocardial oxygen consumption, myocardial lactate extraction, coronary blood flow, myocardial high energy phosphate content and myocardial water content were also studied in order to elucidate the myocardial metabolism. Regarding the myocardial function, no significant difference was observed between the three groups. The results of chemical studies on the myocardial metabolism were as follows: (1) the coronary venous blood pH in group III decreased at the end of the no perfusion period of WBCP. But it thereafter gradually returned to the normal physiological range; (2) the myocardial oxygen consumption in group III increased just after each interruption, but then gradually decreased toward following intermittent WBCP; (3) the myocardial lactate extraction decreased at the end of the non-perfusion period. However, it gradually returned to the control value by the end of each period of WBCP perfusion; (4) after 60 minutes of reperfusion, the coronary venous blood pH, myocardial oxygen consumption and myocardial lactate extraction showed no significant differences between the groups; (5) the coronary blood flow in group III increased significantly after 1 minute of reperfusion; (6) the ATP value in group III decreased significantly after 60 minutes of reperfusion. The ADP and AMP values demonstrated no significant difference between the groups during the same period; and (7) no significant difference was seen in the myocardial water content between the groups after 60 minutes of reperfusion. It is thus concluded that 10 minutes of intermittent WBCP followed by a 15-minute interruption appeared to have no deleterious effect on the myocardial function and metabolism.