For the assessment of stable positions of the electrodes radiographic control, threshold measurements and methods provoking dislocation are used. There is an average dislocation rate of endocardial electrodes of 7-11%. As a further parameter for intra-operative assessment of a stable electrode position intracardiac R-potentials were measured with the stimulation electrode. While QRS complexes in the surface ECG remain unchanged, intracardiac electrocardiograms show an alternating height of the R-amplitude from one ventricular action to the next. From these differences (deltaR) a stable electrode position can be assumed as long as deltaR is small (our patient group 2.12mV+/-1.05MV). Large differences (6.9mV+/-1.7MV) indicate a non-optimal fixation of the electrode tip. The dislocation rate including the post-operative exit block could be reduced below 2% by consideration of the R-amplitude alterations.