Myocardial failure is uniformly fatal when associated with post-traumatic sepsis and multisystem failure. Controversy exists as to whether endotoxin has a direct effect on the myocardium. A nonanoxic isolated arterially perfused rabbit interventicular septum was used in this study to evaluate the effects of endotoxin, liveE. coli, and endotoxin/septic shock plasma on myocardial function and ultrastructure.PurifiedE. coliendotoxin and liveE. colibacteria did not have a significant direct effect on rabbit cardiac muscle function or ultrastructure. Perfusion of the rabbit septum with plasma from rabbits exsanguinated following a 2-hour septic or endotoxin shock insult, however, caused significant (p< 0.02) myocardial depression when compared with control septa perfused with normal rabbit plasma. Septa perfused with shock plasma demonstrated ultrastructural alterations of mitochondria that were not noted in control preparations.