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Brain death often results in a series of hemodynamic alterations that complicate the treatment of potential organ donors before transplantation. The deterioration of myocardial performance after brain death has been described; however, the pathophysiologic process of the myocardial dysfunction that occurs after brain death has not been elucidated. This study was designed to analyze the function of the myocardial @b-adrenergic receptor and the development of left ventricular dysfunction in a porcine model of experimental brain death. Analysis of the @b-receptor included determination of receptor density and adenylate cyclase activity after stimulation independently at the receptor protein, the G protein, and the adenylate cyclase moiety. Myocardial @b-receptor density did not change after the induction of brain death. A decrease in stimulated adenylate cyclase activity was observed within the first hour after brain death at the level of the @b-receptor, the G protein, and the adenylate cyclase moiety, which suggests the occurrence of rapid desensitization of @b-receptor function. Significant deterioration of myocardial performance also occurred within the first hour after brain death, represented by a decrease in preloadrecruitable stroke work compared with the baseline value. The deterioration of myocardial performance after brain death correlates temporally with desensitization of the myocardial @b-receptor signal transduction system. The mechanism of impairment appears to be localized to the adenylate cyclase moiety itself. (J T HORAC CARDIOVASC SURG 95;110: 51)