Background: Tricuspid regurgitation (TR) is often observed in patients (pts.) with low-flow, low-gradient aortic stenosis (LF-LG AS) and low ejection fraction (EF). Its impact on prognosis remains unknown. The objective of this study was to examine the impact of TR on mortality in these pts. Methods: 211 pts. (age=73±10 yrs; 77% men) with LF-LG AS (mean gradient<40 mmHg, AVA ≤0.6 cm2/m2) and low EF (≤40%) were prospectively enrolled and 125 (59%) underwent aortic valve replacement (AVR) within 3 months following inclusion. AS severity was assessed by the projected AVA. The severity of TR was graded according to ASE guidelines. Right ventricular (RV) function was assessed using an integrative approach and classified as normal or reduced. Results: Among the 211 pts., 76 (36%) had TR (24% mild TR and 12% moderate/severe TR). During a mean follow up of 2.4±2.2 yrs, 104 (49%) died. In univariable analysis, TR was associated with an increased risk of all-cause mortality (overall TR: HR=1.82; 95% CI=1.22-2.71; p=0.004; mild TR: HR=1.62; 95% CI=1.02-2.54; p=0.04; moderate/severe TR: HR=2.30; 95% CI=1.27-3.93; p=0.007). After adjustment for risk factors and echocardiographic parameters including RV function, TR was an independent predictor of mortality (overall TR: HR=1.88; 95% CI=1.08-3.23; p=0.02; mild TR: HR=2.19; 95% CI=1.00-4.77; p=0.05; moderate/severe TR: HR=2.68; 95% CI=1.08-6.32; p=0.03). Furthermore, moderate/severe TR was an independent predictor of 30-day mortality following AVR compared to none/trace TR (OR=7.24; p=0.01) and mild TR (OR=4.70; p=0.05). Conclusion: In patients with LF-LG AS and low EF, TR is independently associated with an increased risk of mortality. Moderate/severe TR is associated with increased 30-day mortality following AVR. Further studies are needed to determine whether TR is a risk marker or risk factor of mortality, and whether concomitant surgical correction at the time of AVR can improve outcome in these high risk patients.