To address the nature of inflammatory cells in heart tissue and possible implications in the pathogenesis of heart failure in Chagas' disease, we investigated the number of cells expressing IFN-γ, TNF-α, IL-4, TGF-β, and NOS2 and the levels of FoxP3, STAT4, and STAT6 mRNA in heart tissues of subjects who had died during the chronic phase of the disease. Here, NOS2 is linked to heart failure.