The authors describe the main electrocardiographic features in 90 cases of dilated cardiomyopathy. The patients were divided into tree groups: in group I were the patients with electrocardiographic signs of left ventricular hypertrophy, in group II the patients with complete left bundle branch block and in group III the cases with right bundle branch block, was held in the group I 64 patients (71%), in the group II 22 (24.6%) and in the group III four case (4.4%). Seventy two cases (80%) showed arrhythmias. Atrial fibrillation was observed in 20 patients (28%), supraventricular tachycardia in two (3%), atrioventricular block, of the 1st and 2nd degree, in eight (11%), ventricular arrhythmias in 63 (87.5%) and supraventricular arrhythmias in 42 (58%). In the 64 patients, with left ventricular hypertrophy, 60 (93.75%) showed very important S waves in, at least two right precordial leads. Fourty four patients (73.3%) had rS pattern in right precordial leads, from V1 to V4, with the R waves in V5 and V6 with normal, low and height amplitude. A first degree left bundle branch block was recorded in 16 cases (25%), a pathologic Q waves in 22 (37.5%), low voltage in limb leads in 24 (37.5%), left atrial enlargement in 36 (56%), right atrial enlargement in two (3%) and atrial fibrillation in 10 (16%). In the 22 patients from the group II six (27%) had left atrial enlargement, two (9%) had right atrial enlargement and six (27%) atrial fibrillation. In the four patients from group III two (50%) had an incomplete right bundle branch block, two (50%) the complete form and all had atrial fibrillation.