Objective: Severe secondary tricuspid regurgitation (STR) causes significant right atrial (RA) volume overload, resulting in structural and functional RA-remodelling. This study evaluated whether patients with severe STR and reduced RA function, as assessed by RA-reservoirstrain (RASr), show lower long-term prognosis. Results: A total of 586 patients with severe STR (age 68±13 years; 52% male) were included. Patients presented with mild right ventricular (RV) dilatation (end-diastolic area 13.8±6.5 cm2/m2) and dysfunction (free-wall strain 16.2±7.2%), and with moderate-to-severe RA dilatation (max area 15.0±5.3 cm2/m2); the median value of RASr was 13%. In the overall population, 10-year overall survival was low (40%, 349 deaths), and was significantly lower in patients with lower RASr (defined by the median value): 36% (195 deaths) for RASr ≤13% compared with 45% (154 deaths) for RASr >13% (log-rank p=0.016). With a median follow-up of 6.6 years, RASr was independently associated with all-cause mortality (HR per 5% RASr increase:0.928; 95% CI 0.864 to 0.996; p=0.038), providing additional value over relevant clinical and echocardiographic covariates (including RA size and RV function/size).