Longitudinal prospective study, with a cohort of 100 consecutive outpatient subjects (34 to 74 years old; 31 females) with Chagas' disease followed-up for at least 10 years at the cardiomyopathy outpatient clinic of University Hospital, Rio de Janeiro, RJ, Brazil, a tertiary care center. Enrollment was from 1995 to 1999. Subjects were born in endemic regions of Minas Gerais, Goias or Bahia States of Brazil and Chagas' disease was diagnosed on basis of two positive serum tests, hemagglutination cruzipain-ELISA and indirect immunofluorescence. All subjects were referred to the arrhythmia for risk stratification. At the time of admission none had received nitroderivative therapy. Subjects were classified according to the severity of heart involvement according to Los Andes classification, and divided into three groups: class I - 28 subjects (group 1), class II - 48 subjects (group 2), and class III - 24 subjects (group 3). Clinical and laboratory data were assessed during a personal interview and review of medical records. On admission, all subjects were in New York Heart Association functional class I or II, had normal sinus rhythm and normal PR intervals. Exclusion criteria at initial enrollment were: any degree of atrioventricular block or non-sinus rhythm, previous documented acute coronary events (unstable angina or myocardial infarction), chronic obstructive pulmonary disease, rheumatic valvular heart disease, alcohol addiction, thyroid dysfunction or abnormal serum electrolytes. Treadmill stress test and/or coronary artery angiogram were indicated in selected subjects to rule out concomitant coronary artery disease. World Health Organization and Helsinki Treaty regulations reviewed in Venice (1983) were followed and all subjects provided informed consent to participate.