[Hyperthyroidism and atrioventricular heart block (author's transl)].

Two cases of thyrotoxicosis including a first-degree heart block are reported; a study of action potentials of the bundle of His was achieved in the second case. The association atrioventricular block-hyperthyroidism is unusual but does not seem to be a pure coincidence. The direct effect of thyroid hormon on the myocardium is supposed to be responsible for the conduction disturbance; its disappearance with the cure of the thyrotoxicosis is a favourable argument for a relation of causality. The therapeutic consequence of this association is to exclude completely the use of betablockers.