Chronic Chagas' disease cardiomyopathy is a leading cause of congestive heart failure in Latin America, affecting more than 3 million people. Chagas' cardiomyopathy is more aggressive than other cardiomyopathies, but little is known of the molecular mechanisms responsible for its severity. We characterized gene expression profiles of human Chagas' cardiomyopathy and dilated cardiomyopathy to identify selective disease pathways and potential therapeutic targets. Both our customized cDNA microarray (Cardiochip) and real-time reverse transcriptase-polymerase chain reaction analysis showed that immune response, lipid metabolism, and mitochondrial oxidative phosphorylation genes were selectively up-regulated in myocardial tissue of the tested Chagas' cardiomyopathy patients. Interferon (IFN)-γ-inducible genes represented 15% of genes specifically up-regulated in Chagas' cardiomyopathy myocardial tissue, indicating the importance of IFN-γ signaling. To assess whether IFN-γ can directly modulate cardio-myocyte gene expression, we exposed fetal murine cardiomyocytes to IFN-γ and the IFN-γ-inducible chemokine monocyte chemoattractant protein-1. Atrial natriuretic factor expression increased 15-fold in response to IFN-γ whereas combined IFN-γ and monocyte chemoattractant protein-1 increased atrial natriuretic factor expression 400-fold. Our results suggest IFN-γ and chemokine signaling may directly up-regulate cardiomyocyte expression of genes involved in pathological hypertrophy, which may lead to heart failure. IFN-γ and other cytokine pathways may thus be novel therapeutic targets in Chagas' cardiomyopathy.