The response of the heart during sepsis has been studied in human and animal models with disparate results. Because sepsis induces marked peripheral vascular changes, to accurately determine the cardiac response, one must use indices of cardiac performance that are independent of loading conditions and heart rate. The slope of the end-systolic pressure-diameter relationship (ESPDR) has been proposed to have these properties. Pigs were equipped with transducers to measure left ventricular pressure, internal short axis diameter (D), and pulmonary and coronary artery blood flows. After 7-10 days of basal observations, an endotoxin-loaded osmotic pump delivering endotoxin at 10 micrograms/kg/hr was implanted into each pig. Fourteen pigs were so treated, and 4 expired before 24 hr of endotoxin challenge. In the surviving pigs, cardiac output, heart rate, dP/dtmax, and peak systolic pressures were elevated. However, both ESPDR and % D shortening were both significantly depressed. These data suggest that the cardiac response to chronic endotoxin challenge includes a loss of inotropic state as indicated by the load-insensitive indicator, ESPDR, and confirmed by depressed % D shortening. One possible mechanism for reduced inotropic state during endotoxin challenge could be the loss of coronary perfusion. The surviving endotoxin-challenged pigs demonstrated a significant increase in coronary perfusion while stroke work remained unchanged, suggesting that depressed cardiac inotropic state during endotoxin challenge was not caused by reduced coronary blood flow. Rather, the myocardium was relatively overperfused. Another possible mechanism for the loss of cardiac inotropism during endotoxin challenge may be endotoxin-induced generation of reactive oxygen free radicals. This possibility was tested by measuring total cardiac gluthathione, a cellular component depleted by oxidant stress. Endotoxemia reduced these levels 50%. These results suggest that cardiac injury may be mediated by the generation of reactive oxygen free radicals. Further study will determine if this mechanism participates in the loss of cardiac inotropism during endotoxin challenge.