The aim was to examine the expression of ubiquitin (Ub), 27 kDa heat shock protein (hsp 27) and hsp 60 mRNA in normal and briefly ischemic and reperfused porcine myocardium. The left anterior descending coronary artery was occluded for two periods of 10 min, separated by 30 min of reperfusion. After the second occlusion the myocardium was reperfused up to 210 min. Tissue from ischemic, ischemic-reperfused and nonischemic regions of the heart were analysed by Northern and slot blot hybridization and nuclear run-on transcription assays employing radiolabelled cDNA probes for Ub, hsp 27 and hsp 60 as well as by Western blot using monoclonal antibodies recognizing Ub protein conjugates and antiserum recognizing hsp 27. Systolic wall thickening was significantly decreased at 30 min reperfusion after both occlusions and remained depressed at longer periods of reperfusion. Using Northern blot hybridizations several mRNAs encoding Ub, 0.9 kb mRNA encoding hsp 27, and 2.2 kb mRNA encoding hsp 60 were detected in sham-operated, nonischemic and ischemic myocardial tissues. Densitometric analysis of Northern and slot blot hybridization signals showed the significant increase of the basal tissue levels of Ub mRNA in stunned regions only during the 30 min of the second reperfusion period. Increased levels of hsp 27 mRNA in stunned tissue were already noted at the first ischemic period and were sustained during the subsequent periods of reperfusion as compared to the control region of the heart. Changes in hsp 60 mRNA tissue levels were not observed during ischemia and subsequent reperfusions. Transcription of the Ub and hsp 27 genes was increased during 30 and 120 min of the second reperfusion period. The transient enhancement of tissue levels of Ub mRNA was associated with the temporary formation of new Ub-protein conjugates. However, the increased synthesis of mRNA encoding hsp 27 was not followed by changes of hsp 27 protein content in the myocardial tissue.