Background: Endotoxemia is associated with depressed cardiac function during sepsis. Mesenchymal stem cells (MSCs) possess an ability to modulate the inflammatory response during sepsis, but it is unknown whether MSCs possess the ability to reduce endotoxemia-induced myocardial injury and dysfunction. Methods: Endotoxemia was induced in rats via injection of lipopolysaccharide (LPS). Animals were divided into the following groups: (1) saline + saline; (2) LPS + saline; (3) LPS + MSCs; and (4) LPS + LLC-PK1 renal epithelial cells (differentiated control). At 6 hours, animals were anesthetized, serum was collected, and hearts were extracted and perfused via the isolated heart system. Hearts and serum were analyzed for tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and IL-10. Results: The administration of LPS depressed myocardial function. Treatment with MSCs ameliorated this depression. Serum TNF-α, IL-1β, and IL-6 were elevated in LPS-treated groups. Treatment with MSCs was associated with reduced levels of these cytokines. A trend toward reduced myocardial TNF-α and significant reductions in myocardial IL-1β and IL-6 were observed in the MSC-treated group. IL-10 levels were increased after the LPS administration in both serum and myocardium. Serum levels were increased further after treatment with MSCs. Conclusion: Treatment with MSCs during endotoxemia reduces systemic and myocardial inflammation and is associated with a reduction in LPS-induced myocardial functional depression.