T he pr o tec tive my ocard ial effect of 3 d iffe rent cardio p legic solutions -Br etschneider (HTPI. St . Thomas' Hospital Sol ution (T HOM), Epp endor f so lut io n (EPP) -was investigated in 15 dogs put on extreccrporeet circulation 12 hours of cardiac ischem ia, 3 7 ml /kg card io plegic solution every 30 minutes at 4°el. After the onset of cardio ptegic perfu sion, electric card iac activity was significa ntl y p ro lo nged in the EPP gro up (3 minutesl as com pared with t he HTP and T HO M groups (1.5 minutes). A myocard ial temperature of 15 DC was reached after 5 minutes in EPP as opposed to 3 minutes in HTP and THOM. This can be relate d to a low perfusion rat e in EPP (130 ml/m inutes vs 286 ml/ minutes in HTP and t THOM) due to the high viscosity of t he EPP solution 19.56 centls tok es lest ! vs 1.79 est in HTP and 1.62 est in THOM at 4 DC.After 2 hour s of ische mia, there was marked hyperem ia, low myocard ial 0 2-consumption {MV02 J but no lactate produ ction. After 30 minutes of blood reperfusion, MV0 2 reached the norm al values of the empty bea ting heart in HTP and THOM whereas MV0 2 in EPP stayed low at 1.79 ml/100 g/m inute.In all groups, there was a com parabl e derangement in the autoregulat ion of myocardia l blood flow (MBFI after ischemia ; the init ially close correlation between left ventricular (LVI function and MBF was no longer present.In all groups, postischemic developed peak LV pressure as well as dp/dtma::o: were d iminished by about 40 % at an enddiast olic volume of 30ml.In co nclusion: In co ntrast to results ob tained on isolated hearts, a mod erate functional metabolic impairme nt is observed irrespect ive of the card ioplegic solutio n used when the study is performed under surgical cond itions with ext racorporeal byp ass.