["Exposure of cells to sublethal concentrations of hydrogen peroxide (H2O2) can alleviate subsequent oxidative stress-induced apoptosis. We assessed the effects of H2O2 preconditioning on the therapeutic potential of human umbilical cord Wharton's Jelly mesenchymal stem cells (WJ-MSCs) in a murine model of myocardial infarction.", 'WJ-MSCs were incubated in the media for 2 hours with or without 200 µmol/L H2O2. Mice underwent left anterior descending coronary artery ligation, and received injection of phosphate buffered saline, 1×10(6) WJ-MSCs, or 1×10(6) H2O2 preconditioned WJ-MSCs 3 hours later via tail vein. Echocardiography was performed 0, 7, 14 and 28 days after surgery, and the mice were euthanized on day 28 for histological analysis. In vitro cytokine concentrations in the WJ-MSC cell supernatant were measured by enzyme-linked immunosorbent assay (ELISA). The effect of WJ-MSC cell supernatant on the migration and proliferation of endothelial cells were observed by transwell migration and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazoliumbromide (MTT) assays.', 'Echocardiographic measurements revealed a significant improvement in the left ventricular contractility of the WJ-MSCs-H2O2 group compared to the WJ-MSCs group. Histological analysis revealed increased neovascularization and reduced myocardial fibrosis in the WJ-MSCs-H2O2 group compared to the WJ-MSCs group. Pretreatment of WJ-MSCs with H2O2 increased the secretion of interleukin-6 (IL-6) into the cell culture supernatant by approximately 25-fold. The culture supernatant from WJ-MSCs-H2O2 significantly increased the migration and proliferation of endothelial cells; these effects could be blocked using an anti-IL-6 antibody.'] Does hydrogen peroxide preconditioning enhance the therapeutic efficacy of Wharton 's Jelly mesenchymal stem cells after myocardial infarction?