Introduction: Apoptosis is a main contributor of myocardial reperfusion injury during acute infarction. In a previous study, we showed that reperfusion injury was mediated by the FAS-dependent apoptotic signal mobilizing the DAXX (death-associated protein) adaptor protein. Objective: to evaluate the cardioprotective effects of a synthetic peptide that uncouples FAS to the DAXX downstream pathway.Methods: The SPOT technology was used to design an synthetic peptide interfering with FAS:DAXX interaction. This peptide was couple to the Tat cell penetrating peptide (Tat-DAXXp). Infarct size and apoptosis were evaluated in the left ventricle of mice subjected to a surgical protocol of reversible coronary artery ligation and treated by the peptide at the onset of reperfusion. Cellular internalization of the peptide was measured using a fluorescent peptide by immunofluorescence both in primary cultures of cardiomyocytes or in left ventricles after surgery. Results Anti-apoptotic properties of the synthetic peptide were demonstrated in primary cardiomyocytes. In vivo, one bolus of Tat-DAXXp (1 mg/kg), injected intravenously 5 min before reperfusion in a murine myocardial ischemia-reperfusion model decreased infarct size by 48% after 24 hours of reperfusion. After a 30-min delayed administration, Tat-DAXXp was still able to protect against reperfusion-induced apoptosis and was completely degraded and eliminated within 24 hours thereby reducing risks of potential side effects. Importantly, post-infarction mortality was reduced by 67% by Tat-DAXXp treatment. Mechanistically, cardioprotection was supported by both antiapoptotic and prosurvival effects, and an improvement of myocardial functional recovery as evidenced in ex vivo experiments.Conclusion:Our study demonstrates that a single dose of Tat-DAXXp injected intravenously at the onset of reperfusion leads to a strong cardioprotection in vivo by inhibiting ischemia-reperfusion injury.