The authors report the case of a patient treated with amiodarone for syncopal ventricular tachycardia complicating idiopathic dilated cardiomyopathy in whom symptomatic hyperthyroidism led to a discussion of the different therapeutic options available in this type of case. Neomercazole treatment was prescribed with success enabling maintenance of the antiarrhythmic drug. The reputation of inefficacy of carbimazole should be reconsidered ; high dose therapy should probably be tried in patients with hyperthyroidism when withdrawal of the antiarrhythmic drug does not seem to be possible.