The present study investigated the effect of tumor necrosis factor (TNF)- on myocardial energy metabolism as estimated by myocardial oxygen consumption (MO₂). MO₂ of electrically stimulated isolated trabeculae of right ventricular Wistar rat myocardium was analyzed using a Clark-type oxygen probe. After the initial data collection in the absence of TNF-, measurements were repeated after TNF- stimulation. In separate experiments, pretreatment with the nitric oxide (NO) synthase inhibitor N^G-nitro-L-arginine methyl ester (L-NAME) or the ceramidase inhibitor n-oleoylethanolamine (NOE) was done to investigate NO/sphingosine-related effects. TNF- impaired myocardial economy at increasing stimulation frequencies without altering baseline MO₂. Incubation with TNF- in the presence of L-NAME further impaired myocardial economy. NOE preincubation abrogated the TNF- effect on myocardial economy. Moreover, the negative inotropic effect of TNF- was observed in NOE-pretreated but not L-NAME-pretreated muscle fibers. Exogenous sphingosine mimicked the TNF- effect on mechanics and energetics. We conclude that TNF- impairs the economy of chemomechanical energy transduction primarily through a sphingosine-mediated pathway.