OBJECTIVE: To evaluate asymptomatic patients with chronic Chagas disease to determine prevalence of ventricular arrhythmias, left ventricular dysfunction, and B-type natriuretic peptide (BNP) plasma levels. METHODS: One hundred and six patients from the Chagas disease outpatient clinic underwent clinical evaluation, electrocardiogram (ECG), cardiothoracic index (CTI), ambulatory electrocardiogram (Holter monitoring), echocardiogram, and BNP measurement and then were distributed into three groups: GI, with normal ECG (n = 50); GIIA, with ECG changes characteristic of Chagas disease (n = 31); and GIIB, with other ECG changes (n = 25). RESULTS: The most common electrocardiographic changes were the following. GIIA: complete right bundle branch block (35%), left anterior hemiblock (35%), and electrically inactive areas (32%); GIIB: inferolateral repolarization change (28%), and left ventricular overload (24%). Mean CTI index values were similar (p = 0.383). Ventricular arrhythmia prevalence was higher in the GIIA (77%) and GIIB (75%) groups than in the GI group (46%) (p = 0.002). Ventricular dysfunction was more prevalent in the GIIA (52%) and GIIB (32%) groups than in the GI group (14%) (p = 0.001). Systolic dysfunction was more prevalent in the GIIA group (29%) than in the GIIB (20%) and GI groups (2%) (p < 0.001). Diastolic dysfunction was more prevalent in the GIIA (42%) and GIIB (28%) groups than in the GI group (12%) (p = 0.005). Mean B-type natriuretic peptide levels were 30 +/- 88 pg/mL in the GI group, 66 +/- 194 in the GIIA group and 24 +/- 82 for the GIIB group (p = 0.121), respectively. CONCLUSION: Arrhythmias and left ventricular dysfunction are more prevalent in asymptomatic patients with chronic Chagas disease and abnormal ECG than in patients with normal ECG. Plasma BNP levels were similar among the groups.