Objectives: To clarify the pathophysiologic characteristics of hemorrhagic shock and to assess methods of resuscitation. Design: An animal experiment using sheep subjected to hemorrhagic shock and fibrillation to compare various resuscitation techniques. Setting: An experimental laboratory setting meant to simulate hemorrhagic shock secondary to trauma. Study Groups: Group 1 animals (n = 6) were controls that were not subjected to shock and fibrillation. Group 2 animals (n = 6) were subjected to shock and fibrillation and were resuscitated with volume replacement. Group 3 animals (n = 6) were also subjected to shock and fibrillation but were resuscitated with epinephrine hydrochloride infusion. Group 4 animals (n = 6) were subjected to shock and fibrillation but were resuscitated with cardiopulmonary support. Interventions: The shock was to a mean arterial pressure of 25 mmHg for 1 h followed by 5 min of fibrillation. Group 2 animals were resuscitated for 1 h. Group 3 animals were supported for 6 h on epinephrine after the shock period. Group 4 animals were supported for 1 h on cardiopulmonary support, then were observed for another 5 h. All animals were sedated and intubated, and a median sternotomy was performed. Main Outcomes Measured: Survival, hemodynamic function, lactate production, myocardial blood flow, and water content. Results: Group 1 sheep showed no detrimental effects in any of the measured variables. Group 2 sheep could not be resuscitated. Group 3 sheep could be supported with epinephrine but had a 60% depression in left ventricular function and an ultimately high mortality rate (67%) when the infusion of epinephrine was discontinued. Group 4 sheep had a 100% survival rate and only a 20% deterioration in left ventricular function. Conclusions: Cardiopulmonary support improves survival and preserves left ventricular function compared with volume resuscitation with or without inotropic support in this model of hemorrhagic shock.