['The aim of this study was to assess whether hyperoxic reperfusion contributes to the efficacy of Fluosol 20% or poloxamer 188 for infarct size reduction and whether suppression of polymorphonuclear leukocyte function is responsible for cardioprotection.', 'The perfluorochemical Fluosol and its detergent component poloxamer 188 limit myocardial reperfusion-induced injury; however, the underlying mechanism(s) are uncertain.', 'A series of in vivo and ex vivo studies were performed in a 30-min temporary coronary occlusion rabbit model. Before reperfusion, rabbits received a 25-ml/kg infusion of 1) Fluosol; 2) poloxamer 188 (equivalent % w/v to Fluosol, 675 mg/kg body weight); or 3) 5% dextrose (control). In protocol A, animals were subjected to either normoxic or hyperoxic reperfusion; in protocols B and C, hyperoxic reperfusion was studied. In protocol B, myocardial blood flow was assessed. In protocol C, polymorphonuclear leukocyte function and myocardial myeloperoxidase were determined.', 'In rabbits subjected to normoxic reperfusion, infarct size (normalized to risk region weight) was not significantly different among groups. In rabbits subjected to hyperoxic reperfusion, infarcts were significantly reduced with both poloxamer 188 and Fluosol treatment compared with control animals (p = 0.05 and p = 0.0004, respectively). Blood flow at 3 h of reperfusion within the ischemic endocardium was greater in the Fluosol and poloxamer 188 groups than in the control group (p = 0.001 and p = 0.08, respectively). Myeloperoxidase activity was not affected by treatment, nor was there suppression of polymorphonuclear leukocyte function.'] Is hyperoxic reperfusion required to reduce infarct size after intravenous therapy with perfluorochemical ( Fluosol-DA 20 % ) or its detergent component ( poloxamer 188 ) in a poorly collateralized animal model . Absence of a role of polymorphonuclear leukocytes?