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Objective: Cardiomyopathy and other vascular complications are now recognized as significant components of HIV/AIDS pathogenesis. Although the mechanisms involved in cardiomyopathy are poorly defined, a role for direct retroviral action and/or focal infiltration of activated immune cells have been postulated. Here we investigated mechanisms in retrovirus associated cardiomyopathy using a well-defined mouse model of acquired immunodeficiency. Methods: Mice were dosed with LPBM5 retrovirus; cardiac performance was assessed by echocardiography followed by tissue collection at 5 and 10 weeks post-infection. Results: Contractile deficits were observed at 5 and 10 weeks post-retrovirus infection and preceded the development of overt immunodeficiency. Selective and widespread cardiac infiltration of CD68+ cells, but not neutrophils, mast cells, or eosinophils was also observed at both 5 and 10 weeks. LPBM5 retrovirus was readily detectable in cardiac samples by RT-PCR. Time dependent increases in cardiac protein nitration (biomarker of reactive nitrogen species) were observed and were correlated to the extent of cardiac dysfunction whereas no changes in NOSII occurred at 5 and 10 weeks. We corroborated the mouse findings using cardiac tissues and clinical findings from human HIV/AIDS autopsies. Conclusions: These studies demonstrated that cardiac myocyte protein nitration in AIDS related cardiomyopathies, rather than focal immune cell lesions characterize retrovirus associated cardiomyopathies and differentiate them from non-retroviral cardiomyopathies. [Copyright &y& Elsevier]