Fil: Marin-Neto, José Antônio. Medical School of Ribeirao Preto, University of Sao Paulo, Ribeirão Preto, Sao Paulo; Brasil.Fil: Rassi, Anis. Anis Rassi Hospital, Goiania; Brasil.Fil: Morillo, Carlos A. McMaster University, Population Health Research Institute HGH-McMaster Clinic, East Hamilton, Ontario; Canada.Fil: Avezum, Álvaro. Instituto Dante Pazzanese de Cardiologia, Sao Paulo; Brasil.Fil: Connolly, Stuart J. McMaster University, Population Health Research Institute HGH-McMaster Clinic, East Hamilton, Ontario; Canada.Fil: Sosa-Estani, Sergio. ANLIS Dr.C.G.Malbrán. Centro Nacional de Diagnóstico e Investigación en Endemo-Epidemias; Argentina.Fil: Rosas, Fernando. Clinica A. Saio, Bogota; Colombia.Fil: Yusuf, Salim. McMaster University, Population Health Research Institute HGH-McMaster Clinic, East Hamilton, Ontario; Canada.Benznidazole is effective for treating acute and chronic (recently acquired) Trypanosoma cruzi infection (Chagas' disease). Recent data indicate that parasite persistence plays a pivotal role in the pathogenesis of chronic Chagas' cardiomyopathy. However, the efficacy of trypanocidal therapy in preventing clinical complications in patients with preexisting cardiac disease is unknown.