PURPOSE--It is well established the association between heart failure and arrhythmias in different cardiopathies. There are no studies in Chagas' myocardiopathy that analyze the relation between arrhythmias and left ventricular function. METHODS--We studied 629 patients with Chagas' disease, divided in 3 groups, according to ejection fraction obtained through echocardiographic study (normal, between 0.64 and 0.45, and below 0.44). RESULTS--At conventional ECG, the presence of ventricular arrhythmias was respectively in the 3 groups: 15, 36 and 64, showing higher incidence when left ventricular function was getting worse. CONCLUSION--Ventricular arrhythmias in Chagas' disease are frequent in patients with normal ejection fraction, and become more intense as ventricular dysfunction progresses.