The aim of this study was to compare Chagas and non-Chagas' disease patients using single or dual-chamber pacemaker in relation to the ejection fraction of the left ventricle, the ventricular stimulation threshold and the occurrence of ventricular arrhythmia. From January, 2001 to November, 2002, 45 Chagas' disease patients and 35 non-Chagas' disease patients, all pacemaker users, were evaluated considering clinical history, echocardiographic study, Holter monitoring and analysis of the pacemaker telemetry data. Chagas' disease patients were significantly younger, but both groups were similar when chest X-Ray variables and right ventricular stimulation threshold were analyzed. Chagas' disease patients had a lower left ventricular ejection fraction and more frequent ventricular arrhythmia during Holter monitoring. A positive correlation between the low ejection fraction of the left ventricle and the intensity of ventricular arrhythmia was observed. In conclusion, among pacemaker user patients, Chagas' disease is related to cardiac markers of worse prognosis.