Earlier it has been shown that prophylactic course administration of Rhodiolae rosea extr. - a drug of a group of vegetable adaptogens, short stress effect, adaptation by hypoxia increased the heart resistance to arrhythmogenic exposures that had been accompanied by the increase of the level of endogenous opioid peptides possessing as antiarrhythmic, as well as cardioprotective properties.We evaluated a cardioprotective effect in case of all means of adaptation mentioned above by the degree of 9 9 m Tc-pyrophosphate accumulation in myocardium tissue during administration of toxic doses of isoproterenole (40 mg/kg 24 hours before the experiment). Administration of isoproterenole to intact animals decreased the absorption of radio-active point by more than 4 times. Adaptation of animals significantly decreased the degree of heart damage because of isoproterenole necrosis (p<0,05). Preliminary blockade of opioid receptors by naloxone completely eliminated the found adaptation effect.Thus, the obtained results allow us to affirm that endogenous opioid system plays an essential role in realisation of preventive cardioprotective effect of adaptation.