This study will evaluate the efficacy and safety of benznidazole (an antiparasitic drug) in patients with chronic Chagas' heart disease. Evaluate if benznidazole, an antiparasite drug, given at a dose calculated as 5mg/kg/day for 60 days, now administered as a fixed daily dose of 300mg during 40 to 80 days of treatment - period adjusted according to the patient's body weight to a total minimum dose of 12g (corresponding to 40kg) and a total maximum dose of 24g (corresponding to 80kg) - reduces morbidity and mortality in patients with Chronic Chagas' Cardiomyopathy (CCC). It will be developed in 54 study centres in Argentina, Bolivia,Brazil,Colombia and El Salvador - countries with high incidence of Chagas Disease.