Although many studies of the protective effects of cardioplegic solutions using hypothermia have been conducted, it is also necessary to examine their protective effects under normothermia as regional increases in myocardial temperature during hypothermic arrest are often reported. For this purpose myocardial protection was investigated in the isolated perfused rabbit heart exposed to 60 minutes of normothermic global ischemia during which Krebs-Henseleit, blood with heparin, Tyers', and St. Thomas' Hospital solutions were infused at 0.2 mL/min. Percent functional recovery dP/dtmax (mm hg/sec) at 5 minutes relative to pre-ischemic values using Tyers' (12 +/- 5)% was significantly less (p less than 0.05) than recovery using Krebs-Henseleit (57 +/- 13)% and St. Thomas' Hospital solution (47 +/- 5)%. Recovery using blood (79 +/- 7)% was significantly better than all other solutions. Following 25 minutes reperfusion, 4/6 hearts perfused with Tyers' experienced left ventricular fibrillation, while recovery of developed pressure with Krebs-Henseleit (74 +/- 5.8)%, St. Thomas' Hospital (66 +/- 3.4)% and blood (98 +/- 2.9)% was again significantly improved relative to Tyers', (p less than 0.05). Time to develop 5 mm contracture during the ischemic period was significantly shorter using Tyers' than with the other solutions. Using these indices of function, whereas Tyers' solution provided poor protection, blood provided excellent protection in rabbit hearts under normothermic conditions.