BACKGROUND: Current guidelines consider aortic valve replacement reasonable in asymptomatic patients with very severe aortic stenosis (AS); however, the definition of very severe AS based on peak aortic jet velocity (Vmax) remains unclear with a 5-m/s cutoff in US guidelines and 5.5 m/s in European guidelines. Because ≈20% of patients with severe AS and preserved left ventricular ejection fraction have Vmax in this range, we aimed to assess the relationship between Vmax and mortality and determine the best threshold to define very severe AS. METHODS AND RESULTS: A total of 1140 patients with severe AS (aortic valve area ≤1 cm, Vmax ≥4 m/s) and preserved left ventricular ejection fraction were included. The population was divided into 4 groups according to Vmax (4-4.49, 4.5-4.99, 5-5.49, and ≥5.5 m/s). After adjustment for covariates (including surgery), there was no difference in all-cause mortality between Vmax 4 to 4.49 m/s and Vmax 4.5 to 4.99 m/s (=0.64). Both Vmax 5 to 5.49 m/s and Vmax ≥5.5 m/s exhibited significant excess mortality compared with Vmax 4 to 4.49 m/s (adjusted hazard ratio=1.34 [1.18-1.52]; <0.001, and 1.28 [1.16-1.41]; <0.001, respectively). Mortality risk was similar for Vmax 5 to 5.49 m/s and Vmax ≥5.5 m/s (=0.93). Compared with Vmax <5 m/s, patients with Vmax ≥5 m/s had greater mortality risk (adjusted hazard ratio=1.86 [1.55-2.54]; <0.001), even in the subgroup of asymptomatic even in the subgroup of asymptomatic patients (adjusted hazard ratio=2.08 [1.25-3.46]; =0.005). CONCLUSIONS: Our results demonstrate the strong relationship between Vmax and mortality in patients with severe AS and preserved left ventricular ejection fraction irrespective of symptoms. Vmax ≥5 m/s at the time of AS diagnosis identifies patients with very severe AS at high risk of death.