Introduction: Digitalis toxicity is a common complication in those who are taking this medication, because of its narrow therapeutic window and associated comorbidities. Methods: We present the case of an elderly patient, hypertensive, with chronic respiratory failure due to severe pulmonary fibrosis, found in permanent atrial fibrillation and taking digitalis therapy associated with cardiovascular and respiratory medication. The patient is hospitalized for episodes of palpitations with fast and irregular rhythm accompanied by shortness of breath occurred in the last two months before presentation. Laboratory balance excludes diselectrolitemia and impaired renal and hepatic function. Initial ECG shows a regular narrow QRS tachycardia and ventricular rate of 200/minute, for which was administered digitalis intravenously without getting any change in frequency. Results: The serial electrocardiograms performed in the last two months highlights atrial tachycardia with atrial rate of 200/minute and ventricular conduction 2:1, positive P waves in inferior leads and ventriculophasic alternation of PP intervals, criteria suggestive of digitalis toxicity. Interestingly, in each of these presentations in the emergency department, the patient was treated with digitalis intravenously. The diagnosis was confirmed by digitalis dosage in the laboratory. 24 hours after cessation of digitalis treatment, we found the conversion to sinus rhythm, shortening of QT intervals, ST segment depression in infero-lateral leads and decreasing amplitude of T waves, with subsequent normalization of the ECG tracing until discharge. Conclusions: It is important to recognize the electrocardiographic abnormalities suggestive of digitalis overdose. In digitalis-induced tachyarrhythmias, continued digitalis administration has a very high rate of mortality.