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Abstract Introduction: Resent studies have been shown beneficial effects of hyperoxia pretreatment against ischemia-reperfusion injury in different organs. The aim of the present study was to investigate early and late effects of normobaric hyperoxia (≥95% O2) pretreatment on ischemia-reperfusion injuries in isolated rat hearts. Methods: Following 60 and 180 minutes of hyperoxia, rat hearts were isolated immediately (H60 and H180) or 24 hours later (H60/24 and H180/24), and subjected to 30 minutes of regional ischemia followed by 120 minutes of reperfusion. Incidence and severity of ventricular arrhythmias, mechanical function of the heart and coronary flow were assessed during 120 min of reperfusion. LDH and CK release and infarct size were also assessed. Results: Incidence and severity of reperfusion arrhythmias significantly reduced by hyperoxia pretreatment, especially in the early phase of treanment. H180 reduced the incidence of ventricular fibrillation (VF) to 0% vs. 50% of normoxic control, p<0.05). VF duration decreased in H180 group (0 vs. 50±31s in the NC group, p<0.05) and duration of VT decreased in H60 and H180 groups compared to normoxic control group (NC) (1.5±0.7 s and 7.5±2.5 s vs. 17.7±3.3 s respectively, p<0.05). Hyperoxia improves mycardial contractile function and improves coronary flow during reperfusion. Infarct size and enzymes release were also significantly decreased in early and late phase of hyperoxia pretreatment. Conclusions: These results indicate that hyperoxia pretreatment before induction of regional heart ischemia reduces cardiac infarct size and attenuates reperfusion induced arrhythmias in isolated rat heart. Keywords: Hyperoxia, Ischemia-reperfusion injury, Heart protection, Arrhythmias

Keywords: Hyperoxia, Ischemia-reperfusion injury, Heart protection, Arrhythmias

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