Amiodarone is a very active antiarrhythmic agent, but true incidence of Amiodarone-related side effects is still questionable. In a prospective trial of 400 or 200 mg of Amiodarone day for 56 days in 58 patients, we monitored thyroid and liver function, blood count, chest x-ray, ecg. In addiction we took regularly notice of subjective disturbances and physical signs. Side effects were: conduction disturbances 6%, bradycardia less than 50/min. 2%, gastrointestinal 12%, sleep disorders 12%, hyperthyroidism 4,15% and hypothyroidism 6.25%. Blood levels of Amiodarone and desethylamiodarone were not predictive of side effects. Noteworthy was the absence of cutaneous and pulmonary side effects. On the other hand, thyroid function should be monitored carefully because disfunction is not rare (10.4%) and in the case of hyperthyroidism could be related to worsening of arrhythmias.