Background Entrainment can be useful for mapping atrial tachycardias (ATs) after atrial fibrillation (AF) ablation but may result in AT alteration or termination. Objective We aimed to determine the incidence and risk factors for AT alteration or termination. Methods In 30 consecutive patients, 62 ATs (mean cycle length [CL] 268 ± 53 ms) in which overdrive pacing for entrainment mapping was performed were retrospectively analyzed. AT was classified as altered if the CL or activation pattern remained altered 10 seconds after pacing. The variability in the PP intervals was determined over 10 beats from 2 measures: (1) the difference between the shortest and the longest CL expressed as a percentage of the CL and (2) the mean difference between sequential PP intervals expressed as a percentage of the AT CL (CLDmean). Results Of 386 total pacing attempts (tachycardia CL [TCL] – pacing CL [PCL] difference 15 ± 6 ms), 5 (1.3%) altered or terminated AT and 381 did not change AT (98.7%). When the TCL − PCL difference was ≤20 ms, only 2 of 353 (0.5%) attempts altered or terminated AT. When the TCL − PCL difference was >20 ms, 3 of 33 (9%) attempts altered or terminated AT. The difference between the shortest and the longest CL expressed as a percentage of the CL was significantly greater in ATs that were altered or terminated by pacing than in those unchanged (11.0% ± 9.6% vs 4.5% ± 4.5%; P = .007), but the mean difference between sequential PP intervals expressed as a percentage of the AT CL was not significantly different (3.8% ± 2.6% vs 1.9% ± 2.1%; P = .06). Conclusion Overdrive pacing for entrainment mapping rarely alters or terminates after atrial fibrillation AT, provided that AT is stable before pacing and that the PCL is ≤20 ms shorter than the AT CL.