Even after atrial fibrillation (AF) catheter ablation, many patients still experience relevant symptom burden. The objective of the MENTAL AF trial was to determine whether app-based mental training (MT) during the 3 months following pulmonary vein isolation reduces AF-related symptoms. Patients scheduled for pulmonary vein isolation were enrolled and randomized 1:1 to either app-based MT or usual care. Of 174 patients, 76 in the MT and 75 in the usual care group were included in the final analysis. The intervention was delivered by a daily 10-minute app-based MT. The primary outcome was the intergroup difference of the mean AF6 sum score, an AF-specific questionnaire, during the 3-month study period. Secondary outcomes included quality-of-life measures such as the AFEQT (Atrial Fibrillation Effect on Quality of Life). Mean age (SD) was 61 (8.7) years and 61 (41%) were women. The mean AF6 sum score over the study period was 8.9 (6.9) points in the MT group and 12.5 (10.1) in the usual care group (P=0.011). This referred to a reduction in the AF6 sum score compared with baseline of 75% in MT and 52% for usual care (P<0.001). The change in the AFEQT Global Score was 22.6 (16.3) and 15.7 (22.1), respectively; P=0.026. MENTAL AF showed that app-based MT as an adjunctive treatment tool following pulmonary vein isolation was feasible. App-based MT was found to be superior to standard care in reducing AF-related symptom burden and improving health-related quality of life. URL: https://www.clinicaltrials.gov; Unique identifier: NCT04067427.