Abstract Background Atrial functional tricuspid regurgitation (atrial TR) has received growing recognition as a TR entity with a distinct cause owing to its independence from valvular tethering as the predominant mechanism underlying TR. Atrial fibrillation (AF) is highly prevalent in patients with AFTR and is considered a major contributor to its development. However, evidence on predictors of progression to significant atrial function TR in patients with diagnosed AF is lacking. Methods At a single tertiary university hospital, we studied 11445 patients who underwent echocardiograms at least 1 year apart between 2010 and 2023. Patients with moderate or greater TR at the initial examination (n=432) were excluded to ensure that only subjects with confirmed progression to atrial functional TR were included. Only those with EF > 50%, no other moderate or severe valve stenosis or regurgitation, no valve surgery, and RVSP < 40mmHg were subsequently identified (n= 8159). Patients diagnosed with AF 3 months before or after the echocardiogram were included. The final analysis included 629 patients, 44 progressed to moderate or worse TR during follow-up. Results The mean age of the patients was 68 (62-74) years and 57% were male. The mean time to progression to severe TR was 5.7 years. There was no difference in left ventricle size, ejection fraction of LV, right atrium, and right ventricle size on the initial echocardiogram between the group that progressed to significant TR (group 1) and the group that did not progress (group 2). LA diameter (LAAP), LAV(LA volume), and LAVi were significantly larger in group 1. In particular, the Kaplan-Meier graph of TR progression divided into two groups based on LAV 75ml and LAVi 45ml/m2 showed a significant difference, and in particular, LAVi was a significant predictor compared to other factors. Conclusion In patients with AF, the most common cause of atrial functional TR, an initial LAVi >45ml/m2 was shown to be a predictor of progression to significant TR.cumulative survival rate