BACKGROUND Atrial remodeling associated with atrial fibrillation (AF) is known to be a risk factor for significant tricuspid regurgitation (TR), but the predictor of reversible TR in patients with severe functional TR and AF has been poorly studied. The aim of this study was to investigate the predictors of reversible TR in patients with severe functional TR and AF. METHODS Among 232 patients with severe TR, a total of 71 patients with severe functional TR and AF were enrolled and divided into 2 groups: reversible TR group (n=16, 70.1±15.5 years, 7 males) vs. non-reversible TR group (n=55, 72.3±11.8 years, 20 males). Improvement of TR to moderate or lesser degree on follow-up (FU) echocardiography was considered as reversible TR in the present study. RESULTS During 38.9±26.7 months of FU period, reversible TR was observed in 16 patients (22.5%). The presence of left ventricular (LV) systolic dysfunction was significantly prevalent (43.8% vs. 20.0%, p=0.03) and the improvement in LV ejection fraction (EF) more than 10% on FU echocardiography was more significantly frequent (62.5% vs. 23.3%, p=0.003) in the reversible TR group than in the non-reversible TR group. However, the other echocardiographic parameters, including right ventricular function were not different between the groups. In multivariate analysis using Cox proportional hazard model, the improvement of LVEF more than 10% was the only independent predictor of reversible TR (HR=7.39, 95%CI 1.80-30.28, p=0.005). Nine patients died only in patients with non-reversible TR (12.7%), but the reversibility of TR was not associated with mortality. CONCLUSIONS The improvement of LV systolic function was the only independent predictor of reversible TR. Appropriate medical therapy including management for heart failure should be considered before performing surgery in patients with severe functional TR and AF, especially in patients with LV dysfunction.