With the purpose of establishing clinical and paraclinical differences among chronic chagasic (MCh) and primary dilated cardiomyopathies (MCDP), 96 MCh and 104 MCDP patients with abnormal ECG were submitted to a study protocol which included clinical history, routine laboratory serology for Chagas' diseases, resting ECG, Chest-X-rays, and cardiac catheterisation. Patients with congestive heart failure (CHF) had common clinical and para-clinical findings. However, chagasic patients without CHF showed more prevalence of RBBB and LAH, complex ventricular arrhythmias and more left ventricular dilation while primary dilated cardiomyopathy patients with CHF had predominantly LBBB, simple ventricular arrhythmias, atrial fibrillation and less LV dilation than MCh patients. In order to establish the prognostic value of these findings and response to modern medical therapy, prospective studies on these two groups of patients are needed.