Background : ���Differential pacing��� to confirm counterclockwise conduction block in the cavotricuspid isthmus is a simple method to confirm that block in atrial flutter ablation. However, it sometimes is difficult to obtain reliable results, since good contact of the proximal electrodes of the catheter at the lower lateral wall of the right atrium (lRA) is necessary, and parallel positioning of quadripolar electrodes at the tricuspid annulus is difficult in some patients. Therefore, we evaluated the usefulness of ���differential recording��� instead of differential pacing for that application. Methods and results : Linear ablation of the cavotricuspid isthmus was performed in 27 patients with isthmus dependant atrial flutter. The mean flutter cycle length was 233.9 + 16.6 ms. Five of those were clockwise flutter. Differential pacing, involving pacing from the lRA with the distal and then proximal electrodes or moving the distal electrodes from the lower to mid RA, was performed in all cases. The former method was sometimes very difficult to get good contact of the proximal electrodes against the lRA and the latter was annoying because of the instability of the mapping catheter which should have been fixed at one point such as on the line of block while moving the pacing catheter. We used a simple method envolving moving the mapping catheter toward the CSos and then to the mid or high septum while continuously pacing from a single point on the lRA (Differential recording). Both methods showed the distinct confirmative changes in the distance between the pacing spike and local A electrogram recorded from the mapping catheter after making a complete line of block. A gradual shortening of the distance was maintained until the mapping catheter reached the position of the His in all 26 patients. Conclusion : Counterclockwise conduction block could be confirmed easily not only with differential pacing but also by using ���differential recording���. ���Differential recording��� can be performed reliably unless the mapping catheter crosses above the position of the His.