Introduction: A significant portion of patients with aortic stenosis (AS) have low-gradient AS (LGAS) defined as aortic valve area ≤ 1.0 cm 2 and a trans-aortic mean systolic gradient and peak velocity < 40 mmHg and < 4 m/s, respectively. LGAS has been shown previously to have worse mortality compared to high-gradient AS (HGAS). Etiologies for LGAS include diastolic dysfunction, heart failure, other significant valvular disease, and atrial fibrillation (AF). AF is associated with worse outcomes compared to sinus rhythm (SR) in HGAS. AF is common in LGAS, but whether AF is associated with worse outcomes versus SR in LGAS has not been elucidated. Hypothesis: We hypothesize that AF is associated with higher mortality compared to SR in patients with LGAS. Methods: We retrospectively identified and reviewed charts of patients who were diagnosed with LGAS on transthoracic echocardiogram (TTE) from 2010-2020 at Mayo Clinic. Patient were classified according to rhythm at the time of TTE and history of AF was ascertained among those in SR. Patents were divided into 3 groups; SR without history of AF (group 1), SR with history of AF (group 2), and AF during TTE (group 3). Primary endpoints of overall mortality and cardiac mortality were ascertained. Results: A total of 3400 patients were included: n=2036 in group 1, n=519 in group 2, and n=845 in group 3. After adjusting for age, sex, and the Charlson index, group 2 and group 3 patient had significantly higher overall mortality (HR 1.22 and HR 1.52, respectively, p<0.0001 for both) and cardiac mortality (HR 1.37 and HR 2.05, respectively, p<0.0001 for both), Figure . Conclusions: In LGAS, AF is a significant prognostic indicator of overall mortality and cardiac mortality. LAGS associated with AF may need different management strategies given the higher mortality associated with the presence of AF.