Organ procurement, cold storage and ischemia reperfusion injury (IRI) promote inflammation, which induces endothelial cell (EC) activation and dysfunction post transplantation. EC gap junctions (GJs) breakdown as a consequence of these injuries and play a key role in graft injury post transplantation. Here we explore the therapeutic potential of adding a novel gap junction (GJ) stabilizing peptide, ACT1, to UW preservation solution as a therapeutic agent to improve endothelial cell health. ACT1, is a small peptide Cx43 mimetic, which impairs the association of ZO-1 with Cx43 thus promotes GJ integrity. Mouse cardiac ECs (MCECs) were exposed to 6 hrs of cold storage in UW or UW/ACT1 solution followed by reperfusion to mimic clinical cold storage and reperfusion. Efficacy was determined by trans-endothelial electrical resistance (TEER), a measure of GJ function, cell viability assays, and ELISAs for pro-inflammatory cytokines. In-vivo, utilizing a cardiac allograft model, Balb/c donor hearts were stored in UW or UW/ACT1 for 6 hrs prior to transplantation into C57Bl/6 recipients. Grafts were harvested 48 hrs post-transplant and cardiac graft injury determined by serum cardiac troponin I and histological analyze. Graft inflammation was assessed by immunohistochemistry specific for neutrophil and macrophages. In-vitro studies demonstrate that UW/ACT1 solution significantly reduced EC injury and inflammation, as measured by TEER, cell viability and ELISA. In-vivo studies similarly showed that ACT1 pretreatment of the donor organ led to a reduction in IRI, as noted by reduced serum troponin and histological analysis. Subsequent analysis of neutrophil and macrophage infiltration showed pretreatment significantly reduced graft infiltrates. Taken together these novel findings propose a role for GJ in the pathogenesis of cold storage IRI, and further demonstrate that stabilization of GJ with a novel connexin 43 mimetic, ACT1, significantly inhibits post transplant IRI.