Introduction: The success rate of cavo-tricuspid isthmus (CTI) ablation to treat right common flutter is high, up to 95%, but needs bidirectional block confirmation, requiring 2 or 3 catheters. We describe a new pacing technic using a single catheter to ablate and confirm CTI block with differential PR interval measurements. Methods: We included 61 patients from 5 centers that were referred for CTI ablation. All patients had CTI ablation and the CTI block was confirmed by differential pacing using 2 or 3 catheters. The new method consisted in measuring PR interval on the surface ECG using pacing from the tip of ablation catheter on the lateral side (lateral delay) and septal side (coronary sinus ostium) of the CTI line (difference =delta PR interval) before and after CTI ablation. We analyzed the value of delta PR interval to predict bidirectional CTI block as confirmed by standard methods. Results: Among our patient’s population (63±12 years-old), 39 patients were ablated during sinus rhythm while 22 during common flutter. CTI block was achieved in all patients but one. Then, Lateral delay and delta PR interval increased significantly after validation of CTI block (257±42ms vs 318±50ms and 32±23 vs 96±22ms, p<0.0001, respectively). A cut-off ≥70ms of delta PR interval had a 100% of sensitivity and specificity to predict bidirectional CTI block. Conclusion: A single catheter ablation approach to perform CTI line based on surface ECG PR interval measurement is feasible. After ablation, CTI block