Experimental brain death was induced in 36 chacma baboons. In group A (n=17), brain death was induced with no pharmacologic or surgical manipulation. Group B (n=7) underwent bilateral vagotomy, unilateral left cardiac sympathectomy, or bilateral adrenalectomy before induction of brain death. Group C (n=7) underwent total cardiac sympathectomy. Group D (n=5) was pretreated with verapamil hydrochloride. Following induction of brain death, group A animals were maintained on a ventilator for a mean of 12 hr and 6 hr for the remaining groups. At the end of the experiment, the heart was excised, and tissue blocks were examined with light microscopy at (A) the atriaventricular node-bundle of His; (B) the major coronary arteries; and (C) myocardial tissue from the ventricular septum or left ventricular wall. In group A, 41% of the hearts showed histologic features of injury to the conduction tissue, 70% presented contraction band necrosis of the smooth muscle of the coronary arteries, and an incidence of 100% of the groups showed myocyte injury, more evident in the subendocardial area. In group B animals, conduction tissue injury was seen in 6 animals; the coronary arteries were not examined in this group; the incidence of myocyte injury was seen in 80% of the animals. Animals in groups C and D show no histopathologic injury in the conduction tissue (group A vs. C 2°<0.04), nor in the coronary arteries (group A vs. C P<0.002; group A vs. D PcO.Ol), preserving the myocytes (PcO.OOl). The cathecholamine storm associated to acute increment of the endocranial pressure at the time of induction of brain death induces major histopathologic changes in the myocardium, as a result of endogenous cathecholamines released inducing calcium overflow injury, affecting the conduction tissue, the smooth muscle of the coronary arteries, and the contractile myocardium. This can be prevented by calcium blockers or cardiac denervtion. © 1988 by The Williams and Wilkins Co.