The A. A. show electrocardiagrams of a patient of the chronic cardiac form of the Chagas disease. The ecg varied from time to time, showing at one time a totla ventricula auricle stoppage, at another a ventricular auricle stoppage of the type 2 : 1, at another normal rhythm etc. Besides this, variatios were registered in one single ecg. Two hypothesis were offered to explain these facts: one, in which the toxins would be responisble; another, that there had been an increase in the ventricular refratory period.