The effect of ischemic preconditioning ( IP; 3 min ischemia plus 3 min reperfusion) on the recovery of cardiac function after Ca 2+ depletion was investigated. Isolated rat hearts were subjected to different cycles of IP episodes followed by Ca 2+ free perfusion and repletion. Perfusion of control hearts with Ca 2+ free medium for 5 min followed by repletion of Ca 2+ for 30 min resulted in a marked decrease in the left ventricular (LV) developed pressure and an increase in LV end-diastolic pressure (Ca 2+ paradox). The depressed function due to Ca 2+ paradox recovered with three cycles of IP. Myoglobin release during Ca 2+ repletion also decreased significantly by three cycles of IP. The beneficial effects of IP were also evident when the hearts were subjected to a mild form of Ca 2+ paradox involving 3 min Ca 2+ depletion. The protective effect rendered by IP disappeared when 10 μM of 8-(p-sulfophenyl)-theophylline, adenosine antagonist was perfused for 10 min before IP. These results suggest that IP exerts beneficial effects on Ca 2+ paradox which may be mediated by adenosine.