The Author has studied the electrocardiograms of 6 adult dogs, before and after the inoculation of a Schizotrypanum cruzi strain in these animals, which has been obtained from a human case of Chagas' myocarditis with complete aurriculoventricular block. The acute stage of the disease in these dogs has been observed through frequent examination of recent blood, for the research of the flagelate. Electrocardiogram leads were obtained from before the inoculation to 320 days after it. Beside the peripheral leads, the precordial ones have been taken in some dogs. The interpretation of the electrocardiogram series were done comparatively with the mutabilities of the lead series taken from normal dogs. In all studied dogs there was a marked lowering of voltage in the ventricular complexes, denoting a myocardial lesion. The lowering of voltage of the QRS complexes is already seen in the acute stage as well as through out the transition stage of the disease, reaching the maximum soon after the beginning of the chronic stage. Beside lowering of voltage, there was an electrical axis deviation to the left in two dogs. Ventricular premature beats occurred in one dog and auricular premature beats, in two. In only one dog the P wave showed significant alterations, such as lengthening and notching. The Author points out and discuss the fact that he has not found any alteration in conduction: - there was no lengthening of PR interval and in only one case there was a significant lengthening og the QRS duration. The researches are getting on, being the presented results only partial.