In the framework of a diagnostic cardiac catheterization for the confirmation or exclusion of an idiopathic myocardial disease 72 patients with latent cardiomyopathy (LCM) and 51 patients without pathological haemodynamic parameters (Non-CM) were examined electrophysiologically. Intraventricular and His-Purkinje conduction defects were essentially more frequently to be proved in patients with LCM than in the non-CM group, whereas an increased ventricular vulnerability in the two groups of patients was existing in about 20% of the cases. The disturbances of rhythm anamnestically frequently mentioned by patients with LCM might above all be traced back to atrial dysrhythmias, since in about one third of the examined patients an increased atrial vulnerability could be proved. Prospective studies of the course must explain, whether the pathological electrophysiological parameters are of prognostic importance in patients with LCM.