The function of the isolated perfused rat hearts was studied in four groups of experiments. Group 1--included the hearts of intact animals ("absolute control"), group 2--the hearts of rats subjected to 24 hour immobilization in supine position against the background of triple intramuscular injections of placebo (control), group 3 included the hearts of rats, which during 24 hour immobilization stress were thrice injected a synthetic analogue of endogenous opioids Dalargin in a dose of 3 g/kg, and group 4 included the hearts of animals, which during immobilization were administered Dalargin in a dose of 10 g/kg of body mass. Ulcer index as indicator of stress injury of gastric mucosa was also determined. In the control group of experiments (group 2) 24 hour immobilization stress resulted in complete depression of cardiac performance as compared with group 1, and ulcer index approximated 1. In group 3 the indices of cardiac performance even exceeded those in group 1 (intact animals). As compared with group 2, ulcer index in group 3 decreased by 9 times. In application of Dalargin in a dose of 10 g/kg complete preservation of heart function indices and complete prevention of stress injury of gastric mucosa were also observed. Thus, Dalargin possesses cardioprotective and anti-ulcerogenic effect in immobilization stress in rats. Most probably, this phenomenon can be attributed to its ability to inhibit the activity of sympathoadrenal system, which gets enhanced during stress.