Background: Atrial fibrillation (AF) is the most common form of cardiac arrhythmia. Symptoms include irregular heartbeat, palpitations, lightheadedness, fatigue, short-ness of breath, and chest pain. Self-management options are limited, and patients may seek treatment for acute AF episodes in the emergency department (ED) and may also be hospitalized for AF management. ED visits for AF increased 30.7% from 2007 to 2014, although an increasing proportion of these visits did not require inpatient (IP) admission. AF is increasingly prevalent, but its impact on ED visits and IP admissions in more recent years is not known. Objective: Examine trends in ED visits and IP admissions for AF in the United States since 2014. Methods: This repeated cross-sectional analysis usedED visit and IP admission data from Healthcare Cost and Utilization Project (HCUP)’s Nationwide EmergencyDepartment Sample (NEDS) and Nationwide InpatientSample (NIS) databases (2015-2019) to examine ED visits and IP admissions with a principal diagnosis of AF (International Classification of Diseases, Ninth Revision, Clinical Modification [ICD-9-CM]: 427.31; ICD-10-CM: I48.0x; I48.1x;I48.2x, I48.91) without secondary Atrial Flutter (ICD-9-CM:427.32; ICD-10-CM: I48.3x, I48.4x, I48.92) for adults aged ≥18years. Annual numbers of ED visits and IP admissions were calculated using AHRQ weighted estimates that reflect national estimates. ED visits that resulted in admission to the same hospital were also evaluated. Results: ED visits for AF in the US continued to increase from 2015 to 2019, rising 8.9%, from 550,334 (95% CI:517,844-582824) in 2015 to 599,251 (95% CI: 564,958-633,543)in 2019. Rates of increase were similar for older (≥65 y) and younger (18-64 y) patients. Mean age ranged from 69.6 to69.8 y, with 50.6% to 52.0% of visits for females. The proportion of ED visits that resulted in admission to the hospital decreased over the study period, from 52.7% in 2015 to44.5% in 2019, although IP admissions for AF increased 2%,from 365,835 (95% CI: 352,064-379,606) in 2015 to 372,900(95% CI: 358,330-387,470) in 2019. IP admission numbers declined 7.0% for patients aged 18-64y but increased 5.7%for older patients aged ≥65 y. Conclusions: Annual ED visits for AF have continued to increase since 2014, while ED visits that result in admission have continued to decline. IP admissions have grown more slowly, with declines among younger adults and increases among older adults. Interventions that reduce the need for an ED visit for AF may benefit patients and may be associated with cost reductions. Sponsorship: Milestone Pharmaceuticals Inc.