Objective: We tested whether a decrease in the ratio of anti-inflammatory cytokine, interleukin-10 (IL-10) and Tumor necrosis factor- (TNF-) correlate with the decrease in cardiac function in heart failure. Background: TNF- is suggested to play a role in the progression of heart failure and its effect in many tissues is modulated by IL-10. Any relationship in these two cytokines in heart failure has never been examined. Methods: Coronary artery ligated rats were assessed by both echocardiographic and hemodynamic techniques for their cardiac function at 1, 4, 8 and 16 weeks post myocardial infarction (PMI). Membrane bound and soluble fractions of TNF- and IL-10 proteins, their ratio and their mRNA were analyzed. Losartan was used to modify the function in the 4 W PMI rats to further validate the relationship between IL-10/TNF- ratio and cardiac function. Results: Cardiac function deteriorated with time in all the PMI groups, with a severe failure seen at 16W PMI. Both the TNF- protein fractions were increased in 1 and 4W PMI groups whereas TNF- mRNA was increased in 4 and 8W PMI. Membrane bound IL-10 protein and mRNA were decreased in 4, 8 and 16W PMI groups. The IL-10/TNF- protein ratio decreased in all the PMI groups and this correlated with the depressed cardiac function. Losartan improved cardiac function, both fractions of TNF- and IL-10 proteins, their ratio and IL-10 mRNA. Conclusion: This study suggests that a decrease in the IL-10 and IL-10/TNF- ratio correlate with the depressed cardiac function.