A study was made of the effect of variations in Ca2+ concentration in the perfusate on the function of an isolated heart of control rats and rats exposed to emotional-pain stress (EPS). EPS dramatically enhances the animal heart response to variations in Ca2+ concentration in the perfusate: depression of contractility in response to Ca2+ concentration decrease and higher contractility in response to increased Ca2+ concentration were more pronounced after exposure to EPS as compared to control. It is suggested that increased heart dependence of the animals exposed to EPS is the result of impaired membrane mechanisms of Ca2+ transport in myocardial cells.