In the investigations carried out the value of the noninvasive methods (routine-, three-minute-, 24-hour-, and load-ECG) for the diagnostics of latent ventricular disturbances of cardiac rhythm was controlled. 114 registrations of ventricular arrhythmias according to the Lown-classes with increasingly prolonged periods (1, 6, 12, and 24 hours) show that for the establishment of a ventricular extrasystolia of the classes IV and V a registrations lasting at least 24 hours is necessary. 1- and 3-minute-ECG are not suited for this. The load-ECG has a limited value in the diagnostics of the ventricular arrhythmias. In 155 persons by means of the transoesophageal diagnostic atrial stimulation additionally the sinus node recovery time and the sinuatrial conduction time were determined. In 33 patients of the group with sinus node syndrome the 24-hour-ECG was registered. The sensitivity for the sinuatrial conduction time is 75% and for the sinus node recovery time is 82%. Altogether the two investigation methods, the non-invasive electrophysiology and the long-term ECG, allowed to make a correct diagnosis in 94% of the patients with sinus node syndrome.