The autonomic nervous system plays an important role in the genesis of various cardiac rhythm disorders. Experimental studies have indicated that in atrial fibrillation particularly vagal activity may have a decisive influence on the electrophysiologic properties of atrial myocardium. In patients with paroxysmal atrial fibrillation, a carefully taken history and electrocardiographic findings obtained during Holter monitoring can help to distinguish vagally mediated from adrenergically mediated atrial fibrillation. The former is considered to represent a form of lone atrial fibrillation affecting particularly males aged 40 to 50 years. The arrhythmic episodes manifest themselves most often during the night lasting from minutes to hours. There is a lack of tendency towards the development of permanent atrial fibrillation. Digitalis glycosides or beta-receptor antagonists are not helpful in the therapy of this form of atrial fibrillation whereas class I antiarrhythmic drugs have been shown to be more effective. Adrenergically mediated atrial fibrillation is in general less frequently observed than the vagally-induced form. In patients with episodes of atrial fibrillation provoked by emotional or physical stress, the diagnosis of adrenergically mediated atrial fibrillation should be suspected. The episodes of atrial fibrillation occur mostly during daytime. beta-receptor antagonists play a major role in the treatment of this form of atrial fibrillation.