This paper reports a patient with Wolff-Parkinson-White syndrome who presented with a tachycardia showing an unusual QRS morphology closely resembling that of a ventricular tachycardia. On reversal to a normal rhythm the electrocardiogram showed changes of a type A preexcitation, with subsequent conversion to a type B pattern. This phenomenon was observed on two separate occasions. Such conversion would suggest the presence of two distinct sites for bypass location resulting in preexcitation, thus lending support to the theory of aberrant atrioventricular conduction via a bundle of Kent or neuromuscular tissue connecting atrium to ventricle. The configuration of the QRS complexes during the tachycardia would appear to be due to a circus movement with antegrade anomalous atrioventricular conduction and retrograde atrial stimulation via the bundle of His, although in this case, due to the presence of two distinct anomalous atrioventricular conduction pathways, both antegrade and retrograde conduction via these two pathways alone cannot be excluded.