Background Current American Heart Association/American College of Cardiology/Heart Rhythm Society guidelines and European Society of Cardiology guidelines recommend antiarrhythmic drugs (AADs) for maintenance of sinus rhythm in patients with atrial fibrillation. We assessed the concordance between healthcare provider real-world practice and current guidelines with respect to first-line AAD rhythm management. Methods and Results Administrative claims data from the deidentified Optum Clinformatics Data Mart database were used. Patients were included if they were initiated on an AAD in 2015 to 2016, had 1 year of continuous data availability before their first AAD pharmacy claim, and had a diagnosis for atrial fibrillation within that period. Concordance was assessed by comparing the AAD initiated by the healthcare provider against guideline recommendations for first-line treatment, given the presence of heart failure, coronary artery disease, both, or neither (as determined by and [ and ] codes). Concordance was also assessed by provider type using Medicare taxonomy codes. For the 15 445 patients included, 51% of healthcare providers initiated AAD treatments with amiodarone, 18% flecainide, 15% sotalol, 8% dronedarone, 5% propafenone, and 2% dofetilide. The overall rate of guideline concordance was 61%, with differences by provider type: 67% for electrophysiologists, 61% for cardiologists, and 60% for others (internal medicine, etc). Conclusions There continues to be a sizable gap in concordance between practice and guidelines in first-line rhythm management of patients with atrial fibrillation. Further research is needed to identify possible explanations for non-guideline-recommended use of AADs, in addition to enhanced AAD educational strategies for practitioners.