INTRODUCTION: Recurrent atrial flutter following cavotricuspid isthmus (CTI) ablation remains a significant problem. The prevalence of low contact force (CF) during CTI ablation using standard tools is unknown. Our aim was to characterize the prevalence of low CF applications when experienced operators performed CTI ablation using "traditional" markers of contact blinded to CF measurements. METHODS AND RESULTS: Average CF (grams, g) and force-time integral (FTI) was analyzed in 458 lesions in 17 patients undergoing CTI ablation. The isthmus was divided into the annular, mid and caval segments for region-specific analysis. Despite "good" contact using traditional markers, there was significant variability in CF within each isthmus segment (e.g., annular CTI 1-57 g). A high proportion of lesions had a CF <10 g (40%). Lowest CF was the annular (median 9 g), followed by the mid (12 g) and the caval CTI (18 g, P < 0.001). Sites of acute CTI re-connection had a lower average CF and FTI than nonreconnected sites (P < 0.05). Each 1 g increase in CF was associated with a 16% reduction in risk of recovered CTI conduction (95% confidence interval: 4-27%, P = 0.01). CONCLUSION: Use of surrogate markers of "good contact" during ablation by experienced operators in the absence of real-time CF sensing resulted in nearly half of all lesions being delivered with low CF with marked region-specific variability in CF. Low CF was implicated in longer time to achieve conduction block and increased risk of acute reconnection. These findings underscore the importance of real-time CF measurements for optimizing ablation of typical atrial flutter.