BACKGROUND: The objective of this study was to evaluate different tests of heart viability in a pig model of warm ischemia. METHODS AND RESULTS: Pig hearts (n = 30) were submitted to 0 (= group I), 10 (group II), 20 (group III), 30 (group IV), and 60 (group V) minutes of in situ warm ischemia (animal exsanguination). Hearts were removed, then flushed with cardioplegic solution for 3 minutes at a fixed pressure of 60 cm H2O, and edema formation, initial coronary flow, and ionic composition (Na+, K+, and Ca++) of coronary sinus effluent were evaluated. Hearts were then stored for 2 hours in a cold (4 degrees C) preservation solution. Myocardial biopsies (and evaluation of energetic index) were performed, then the hearts were reperfused for 30 minutes with whole blood with an in vitro functional testing system. No edema occurred during cardioplegic flush in the hearts in groups I through IV, but a 37 +/- 11% weight increase (P < .001) occurred in hearts in group V. There was a progressive decrease in initial coronary flow with the increase in the duration of warm ischemia (70 +/- 14 mL/min per 100 g of tissue in group I and 52 +/- 9, 41 +/- 16, 25 +/- 11, and 23 +/- 5 mL/min per 100 g, respectively, in groups II through V (P < .01 to P < .001 versus group I). Initial coronary flow was positively correlated with the energetic index (r = .84, P < .001), and the left ventricle developed pressure at reperfusion (r = .90, P < .001). Finally, there were significant differences between hearts in the control group and those in group V for calcium and sodium release (lower in the control group; P < .001 and P < .01, respectively) and for potassium removal (lower in group V, P < .05). CONCLUSIONS: These data suggest that early measurement of coronary flow after removal of the heart may help to assess heart viability before transplantation. This approach may provide a comprehensive clinical evaluation to increase the number of hearts available for transplantation among those that are rejected in the absence of accurate criteria of viability.