Out-of-hospital cardiac arrest (OHCA) remains a severe health problem in the United States. More than 350,000 patients die or have severe neurological deficits each year despite best efforts in cardiopulmonary resuscitation (CPR). Although successful resuscitation and outcome are inversely proportional to the duration of OHCA, we have reason to believe that the abrupt molecular and metabolic changes resulting from reintroduction of blood flow during initial CPR are more harmful than the injury caused by the ischemia itself. Accordingly, for this competitive Transformative Research Award we propose several novel and readily applicable strategies to mitigate the development of reperfusion injury (RI): ischemic postconditioning (IPC), i.e., controlled pauses of blood flow by intermittently stopping chest compressions, and pharmacological postconditioning with inhaled agents (IAPC) such as sevoflurane or helium administered through the lungs during the first 3 min of CPR. Though seemingly contradictory and challenging current standard-of-care CPR, we submit, however, that the proposed study of mechanisms, safety, and efficacy of these protective techniques against RI could fundamentally change traditional clinical paradigms. In pursuit of our overall goal to improve neurologically intact survival for OHCA for thousands of patients each year, the objectives of our proposed project are to test different postconditioning strategies (IPC, IAPC) and their combination, to characterize their organ-protective development over time, and to elucidate their intracellular signaling mechanisms. Based on preliminary results, we hypothesize that increased nitric oxide production and delayed mitochondrial permeability transition pore opening are responsible for the dramatic improvement in animals when resuscitated with IPC and/IAPC compared to standard CPR. In three staggered specific aims we will assess cardiac, cerebral, renal and hepatic protection by integrating early and delayed IPC and IAPC into CPR following prolonged ventricular fibrillation in an established pig model. Results will be compared with the current gold-standard of therapeutic hypothermia. State- of-the-art hemodynamic measurements, organ-specific biomarkers, tissue histology, mitochondrial studies and neurological testing will provide a comprehensive quantitative and qualitative assessment of the observed protection in each system. Convincing preliminary evidence together with the wealth of expertise of researchers from three different academic institutions make this a most promising, innovative and unique approach whose results offer exceptional potential to influence research and clinical care in the field of resuscitation for yeas to come.