We estimated the correlation of myocardial temperature, intramyocardial pH, and myocardial electrical activity (MEA) during hyperkalemic hypothermic cardioplegic arrest to functional recovery after reperfusion to assess those parameters as intra-operative on-line assessment of myocardial preservation during cardiac operation. Twenty dogs underwent cardiopulmonary bypass at 30 degrees C. Cardiac function was evaluated before and after two hours ascending aortic cross-clamping. The dogs were divided into four groups according to cardiac preservation methods employed. Group I (n = 6): 4 degrees C hyperkalemic crystalloid cardioplegic solution was delivered antegradely through the aorta every 30 minutes without topical cooling. Group II (n = 4): total volume of cardioplegic solution same as Group I was delivered only once without topical cooling. Group III (n = 5): cardioplegic solution same as Group I with lidocaine (100 mg/l) was delivered every 30 minutes without topical cooling. Group IV (n = 5): cardioplegic solution same as Group I was delivered every 30 minutes with topical cooling. Hearts at less than 8 degrees C during aortic cross-clamping (Group I) revealed better functional recovery (72 +/- 21%) than those over 15 degrees C (Group II-IV, 28 +/- 30%). There was no significant correlation between intramyocardial pH changes during aortic cross-clamping and functional recovery after reperfusion (R = -.2257). During aortic cross-clamping, the occurrence of MEA which was obtained directly from the electrode inserted into left ventricular anterior free wall (direct MEA) was observed in all cases. However the myocardial activities which were identified by direct MEA were not necessarily observed visually or by routine electrocardiogram.(ABSTRACT TRUNCATED AT 250 WORDS)