In the submitted case-history the authors describe Conn’s syndrome. A solitary cortical adenoma was involved manifested at first by so-called „lone“ atrial fibrillation (idiopathic without organic causes). The trigger factor of the life threatening ventricular tachycardia were variable values of serum potassium and treatment of atrial fibrillation by anti-arrhythmic drugs.

        Key words: Conn’s syndrome - Arrhythmia.