This is the same patient in the electrophysiology laboratory. A ventricular catheter is used to stimulate the ventricle and a right atrial (RA) catheter is used to record the atrial activity. The patient has been premedicated with digoxin 0.25mg/day. The tracing shows four surface leads and one intra cardiac recording. Supraventricular tachycardia is induced with a train of ventricular beats and a final premature beat. Note that the last stimulated beat has a shorter pacing interval and results in a longer interval between it and the next RA deflection. This then sets off AVNRT with the RA activity now closely associated with the QRS. The short-long interval between the initiating beat and the first QRS of the tachycardia is similar to that of the spontaneous tracing. The long interval suggest conduction down a slow anterograde pathway which is typical of AVNRT.