Exposure of cultured heart muscle cells to noradrenaline led to a decrease in the effects of isoproterenol and prostaglandin E1 on cAMP formation and contraction velocity. However, heterologous desensitization, as measured by prostaglandin E1 stimulation, only occurred at higher noradrenaline concentrations than homologous desensitization (isoproterenol stimulation). As the defects of the adenylate cyclase system in heart failure are attributed to noradrenaline-induced desensitization, it is concluded from the results that, in comparison to the subsensitivity to beta-adrenoceptor agonists in failing human hearts, a decrease in the responsiveness to other receptor-dependent adenylate cyclase stimulators should also occur but only at higher degrees of heart failure.