Atrioventricular (AV) node reentry has been recognized as a clinical arrhythmia for many years. Earlier basic investigations identified a dual AV conduction system, and atrial echo beats occurred when the refractory period of the slow conduction pathway was shorter than the fast pathway. Subsequent studies in humans confirmed the concept of dual AV node physiology and AV node reentry. Slow-fast AV node reentry (anterograde conduction over the slow pathway and retrograde conduction over the fast pathway) occurs most frequently. The fast-slow and intermediate varieties are much less common. A high (> 95%) cure rate occurs with radiofrequency catheter ablation with experienced electrophysiologists. Most electrophysiologists prefer the posterior approach, which results in absence or very poor conduction over the slow AV node pathway: the PR interval is minimally changed. This approach is highly successful for all three forms of AV node reentry and associated with a 1%-2% incidence of heart block in most experienced laboratories.