Background: Atrial fibrillation (AF) is the most prevalent arrhythmia leading to hospital admissions. The majority of patients with AF report symptoms that are believed to be associated with the arrhythmia. The symptoms related to AF traditionally are collected during a clinic visit that is influenced by biases associated with recalling the experience over a limited period of time. Purpose: We designed this pilot study to assess the usability and feasibility of a mobile application to assess symptoms in patients with AF. Methods: We designed a mobile application (miAfib) to assess symptoms (chest pain, palpitation, shortness of breath, fatigue, dizziness/lightheadedness), positive affect (happy, excited, content) and negative affect (worried, angry, sad) on multiple occasions throughout the day based on iOS platform. We performed a four-week feasibility trial to examine user adherence, acceptance and experiences with the mobile application. We administered questionnaires to assess factors affecting usage and self-reported acceptance of the application based on a five-point Likert scale with zero representing strongly disagree and 5 representing strongly disagree with. Results: We included ten patients with paroxysmal and persistent AF. The mean number of completed assessments each day was 2.81  1.59 with 94.7% of days with at least one assessment. The users found the application easy to use (4.750.46), intended to use it in the future (4.371.06) and found it easy to integrate into daily routine (4.51.07). Conclusions: In this pilot study, we found participants in this four-week trial reliably used the application and were able to use the app to report their daily symptoms and affect regularly. Participants reported that they found the application easy to use and would consider using the application in the future.