Cells subjected to increases in temperature induce the expression of several proteins known as heat shock or stress proteins. This process enhances the cell's ability to overcome the effects of further stress. In this respect, the effects of heat stress have been reported to protect the hearts of rats following ischaemia and reperfusion. We have confirmed and extended this observation, not only using different indices of myocardial injury but also in another species, namely the rabbit. Animals were anaesthetized and the body temperature raised to 42 degrees C for a 15-min period. Controls were treated in the same way but without heating. Twenty-four hours later the rabbits were re-anaesthetized and the hearts removed for either heat stress protein analysis or perfusion with Krebs buffer using an isolated perfused heart apparatus. Hearts were subjected to 60 min of low flow (1 ml/min) ischaemia followed by 30 min of reperfusion. All hearts subjected to heat stress showed an enhanced recovery of function upon reperfusion as measured by improvements in developed pressure (27.3 +/- 3.6 vs 16.3 +/- 3.0 mmHg) and diastolic pressure (37.3 +/- 7.4 vs 54.7 +/- 3.1 mmHg). In addition, creatine kinase release, associated with reperfusion, was significantly reduced in the heat-stressed hearts (532 +/- 102 vs 1138 +/- 73 mU/min/g wet wt). Myocardial accumulation and release of oxidized glutathione, an index of oxidative stress, was significantly reduced in the heat-stressed group (0.003 +/- 0.003 vs 0.376 +/- 0.113 nmol/min/g wet wt). The improved metabolic status of the reperfused heat-stressed hearts was further demonstrated by a significant conservation in the levels of ATP (6.1 +/- 0.9 vs 2.8 +/- 0.8 mumol/g dry wt) and CP (36.9 +/- 6.4 vs 16.4 +/- 5.1 mumol/g dry wt). Finally, isolated mitochondrial function in terms of respiratory control index (RCI) was maintained in the heat-stressed hearts (9.2 +/- 0.9 vs 5.7 +/- 0.2) and overloading with calcium was reduced. These data extend the hypothesis that heat stress protects the heart following ischaemia and reperfusion in this in vitro model, in a way as yet undetermined.