Heat shock protein (Hsp) 70s including Hsp72 and Hsp73 are suggested to play an important role in the cardioprotection against stress-induced functional damage. Myocardial tolerance against ischemia/reperfusion injury is increased when myocardial Hsp72 is accumulated after an exposure of normal animals to heat shock. Post-ischemic contractile recovery is improved in the perfused heart of Hsp72-overexpressed mice. However, the role of Hsp72 and Hsp73 in the failing heart following acute myocardial infarction remains unclear. The present study was undertaken to determine whether Hsp72 and Hsp73 production may contribute to the protection of cardiac function in rats with chronic heart failure (CHF) following coronary artery ligation (CAL). The rats with CAL revealed the signs of CHF at the 8th week after the operation. The hearts isolated from rats with CHF were perfused and then subjected to heat shock (at 42 degrees C) for 15 min followed by 6-h perfusion (HS group). The cardiac function of the HS group was markedly decreased and the heat shock-induced increase in myocardial Hsp72 and Hsp73 was attenuated after 6-h perfusion. In the CAL rat treated with the ACE inhibitor trandolapril from the 2nd to the 8th week, induction of Hsp70s was preserved and heat stress-induced reduction in cardiac function was attenuated. The results suggest that a reduction in the production of Hsp70s may play a significant role in the decrease in contractile function during the development of heart failure.