Electrophysiological studies with extrastimulus technique demonstrated evidence of dual A-V pathways in two patients with paroxysmal supraventricular tachycardia (PSVT). In case one, the second P of paced Wenckebach sequences was followed by two conducted QRS complexes without an intervening P wave. The A-H of the first and second QRS were consistent with the fast and slow pathway conduction times. The second QRS was followed by an atrial echo and PSVT, suggesting that the first pathway was available for retrograde propagation following the second QRS. In case two, PSVT was induced with atrial extrastimulus, followed by development of A-V dissociation. The two cases suggest the following conclusions: (1) dual A-V nodal pathways may allow the occurrence of double antegrade conduction of one P; (2) the atria are not necessary for A-V nodal circus movements in "dual pathway" A-V nodal reentrant PSVT.