['Acute treatment with bone marrow mesenchymal stem cells (MSC) reduces myocardial infarct size by multiple mechanisms, including the paracrine release of protective growth factors. Female MSCs produce more growth factor when stressed; therefore, we hypothesized that myocardial protection provoked by female MSCs would be greater than that elicited by male MSCs.', 'Hearts were subjected to 25 min of warm global ischemia, 40 min of reperfusion, and randomly assigned into one of three groups: (1) vehicle treated; (2) male MSC treated; and (3) female MSC treated. Myocardial function was continuously recorded and in separate experiments, male and female MSC growth factor production was assessed by ELISA.', 'All indices of functional recovery were significantly higher in the stem cell infused rat heart compared with control hearts. Interestingly, female MSC treated rat hearts demonstrated significantly greater recovery of left ventricular developed pressure, +dP/dT, and -dP/dT than male MSC treated hearts at end reperfusion. In addition, male MSCs produced significantly greater tumor necrosis factor alpha, and significantly less vascular endothelial growth factor than female MSCs.'] Is in the adult mesenchymal stem cell population , source gender a biologically relevant aspect of protective power?