The first report about successful radio frequency ablation of a right-posterior-septal accessory pathway appeared in 1986. Since then, the technology of both guidable ablation catheters and radio frequency generators has been considerably improved in an initially clinical-experimental phase. At the same time, electrophysiologists were equally able to enlarge their knowledge in the field of signal characteristics of arrhythmogenic substrates. This included the discovery of action potentials of accessory pathways (preexcitation syndromes), the location of fast and slow AV node conduction (AV nodal reentrant tachycardia, AVNRT), the functional importance of the anatomical isthmus between the os of the coronary sinus, the tricuspid valve and the inferior caval vein (atrial flutter). Mapping techniques such as transient and concealed entrainment became, among others, significant tools in finding the best localization for radio frequency catheter ablation. Thus, technical development and the increased knowledge of clinical electrophysiologists resulted in firmly establishing the procedure of catheter ablation as the method of first choice in the curative treatment of supraventricular tachycardias in a potential collective of about 5 per mill of the normal population (without atrial fibrillation). Supraventricular tachycardias with a reentry mechanism in the broadest sense (> 95% of all pts. with SVT) and those with focal automaticity (< 5%) occur as atrial fibrillation or atrial flutter in about 60% of all pts. (4-6 per mill of the normal population). Manifestation of the remaining reentrant tachycardias is mainly in the form of AVNRT (retrograde conduction via the fast pathway > 90% versus uncommon type < 10%). AV reentry via accessory pathways is found in about 15%, with orthodromic conduction via the AV node (> 90%). Atrial reentrant tachycardias are rather rare (with the exception of atrial fibrillation/flutter). The literature suggests medical therapy to be successful in about 60% of these patients. Those patients who are presently proposed to receive radio frequency catheter ablation usually continue to be symptomatic despite pharmacological therapy and/or have a potential risk for sudden cardiac death due to atrial fibrillation in WPW syndrome, or rate-dependent hemodynamic compromise secondary to cardiac disease. Since 1989-1995, our laboratory had a > 93% success rate in treating 466 patients with AV reentrant tachycardia via accessory AV pathways, and in treating 398 patients with AV nodal reentrant tachycardias. Forty patients with atrial flutter and 16 patients with different atrial tachycardias (14 with focal origin, 2 reentries) were free from tachycardia in 80% after ablation. This corresponds to the literature published by other centers. Some abstracts and articles suggest that ablation of atrial fibrillation may be possible. However, there is still a lack of basic experience with view to mapping procedures and, thus, insufficient knowledge of the electrophysiological pathophysiology with regard to different cardiac diseases. As a consequence, this procedure, despite first documentation of both successful treatment and severe complications occurring in catheter ablation of atrial fibrillation, as based on the experience of the MAZE procedure, is applied in humans, at the time being, in a purely experimental setting. The only exception relates to the ablation of the AV node at accurate diagnosis for pacemaker implantation (VVIR; DDDR switch mode) which has become part of routine therapy, although, of course, atrial fibrillation itself or necessary anticoagulation cannot be abolished. Thus, our center shows a success rate of 98% in treating 117 patients by this method. First promising reports are available describing the attempt of AV node modification in the posterior nodal part with the goal of reducing the ventricular rate in atrial fibrillation.