Background: 15-F_2t-isoprostane is a specific marker of in vivo lipid peroxidation induced by reactive oxygen species (ROS) whose formation is increased after myocardial ischemia and during the subsequent reperfusion. 15-F_2t-isoprostane possesses potent bioactivity under pathophysiological conditions. However, it remains unknown whether 15-F_2t-isoprostane, by itself, can influence myocardial ischemia-reperfusion injury (IRI). Methods: Adult rat hearts were perfused by the Langendorff technique with Krebs-Henseleit solution (KH) at a constant flow rate at 10 ml/min. 15-F_2t-isoprostane 100 nM (IsoP), SQ 29548 1 µM (SQ), a thromboxane receptor antagonist that can abolish the vasoconstrictor effect of 15-F_2t-isoprostane, or their combination (IsoP+SQ) in KH or KH alone(vehicle control) were applied for 10 min before inducing 40 min global ischemia, followed by 60 min of reperfusion. During ischemia, saline (control), IsoP, IsoP+SQ or SQ in saline was perfused through the aorta at 60 µl/min. Either IsoP, IsoP+SQ or SQ in KH were infused during the first 15 min of reperfusion. Results: Coronary effluent endothelin-1(ET-1) concentrations in the IsoP group were significantly higher than those in the control group during ischemia and also in the later phase of reperfusion (P<0.05). Infusion of 15-F_2t-isoprostane resulted in increased release of cardiac-specific creatine kinase (CK-MB) and reduced cardiac contractility during reperfusion and also increased myocardial infarct size relative to the control group. SQ 29548 abolished the deleterious effects of 15-F_2t-isoprostane. Conclusion: 15-F_2t-isoprostane exacerbates myocardial IRI, and may therefore act as a mediator of IRI. 15-F_2t-isoprostane induced ET-1 production during cardiac reperfusion may represent a mechanism underlying the deleterious actions of 15-F_2t-IsoP.