Three cases of pacemaker interactive tachycardia are presented. The first two are [artificial] circus movement tachycardias. In the first one the retrograde arm of the tachycardia circuit was provided by the A-V node and the antegrade arm by an atrial synchronous pulse generator. In the second case, the A-V node and, coincidentally, an A-V sequential pulse generator alternately provided the antegrade arm while the retrograde arm was by way of an accessory pathway. In the third case ventricular inhibition during A-V sequential pacing gave the paced atrial events the chance to be conducted to the ventricles with a long A-V interval. This resulted in a tachycardia with a rate of 150 bpm, instead of the programmed rate of 110 bpm.