In view of the cardloprotective effect of oxytocin (OT) released in response to stress, the aim of this stud y was to evaluate the role of heat shock proteins Hsps 70, 27 and 20 in stress-induced cardioprotection in isolated, perfused rat hearts. Rats were divided in two main groups: unstressed and stressed rats, and all of them were subjected to i.c.v, infusion of vehicle or drugs: unstressed rats (control: vehicle, OT (100 ng /5 μl), atosiban (ATO; 4.3 μg/5 μl) as OT antagonist, ATO+OT I, and stressed rats 1St: stress, OT+St, ATO+Stl. After anesthesia, hearts were isolated and subjected to 30 min regional ischemia and 60 min subsequent reperfusion (TR), Acute stress protocol included swimming for 10 min before anesthesia. Malondialdehyd e in coronary effluent was measured and the expression of Hsp 70, 27 and 20 was measured in myocardium using re al-time reverse transcriptase polymerase chain reaction (RT-PCR). The ma londialdehyde levels, which decreased in the St and OT groups, increased by the administration of atosiban as an OT antagonist. The expression of Hsp27 increased 4 to 5 folds by stress induction and i.c.v. infusion of OT. Central administration of atosiban prior to both stress and OT decreased Hsp27 mRNA levels. These finding s suggest that endogenous OT may participate in stress-induced cardioprotection via Hsp27 over-expression as an early response.