AIMS:Previous studies using echocardiography suggested that a low flow (LF) defined as an indexed stroke volume (SVi) <35 mL/m(2) may be an important determinant of outcome in patients with severe aortic stenosis (AS). We sought to assess the prognostic importance of stroke volume derived from invasive data. The aim of this study was to determine the impact of LF, purposely derived from cardiac catheterisation data, on outcome of patients with severe AS and preserved LVEF. METHODS:Between 2000 and 2010, 768 patients with preserved LVEF (>50%) and severe AS (valve area ≤1 cm(2)) without other valvular heart disease underwent cardiac catheterisation. The long-term overall mortality was assessed as the primary end-point. RESULTS:Mean age was 74±8 years, 58% were men, 46% had coronary artery disease and mean LVEF was 72±10%. Low SVi was found in 27% (n=210) of patients with AS. As compared with patients with normal SVi, those with low SVi were significantly older (p<0.0001) with higher rate of atrial fibrillation (p<0.0001). Additionally, they had lower LVEF (p=0.046), aortic valve area (p<0.0001), mean pressure gradient (p<0.0001), systemic arterial compliance (p<0.0001) and higher systemic vascular resistances (p<0.0001). Eight-year survival was significantly reduced in patients with low SVi as compared with those with normal SVi (51±5% vs 67±3%; p<0.0001). After adjustment for all other risk factors, reduced SVi was independently associated with long-term mortality (HR=1.45, 95% CI 1.1 to 2.1; p=0.048). CONCLUSIONS:In patients with severe AS and preserved LVEF, LF, as assessed using cardiac catheterisation is frequent, and is an independent predictor of mortality. Consequently, the measurement of SVi should be systematically included in the assessment of these patients.