Objective: To access the prognostic value of cardiopulmonary exercise testing (CPX) in patients with asymptomatic or equivocal symptomatic aortic stenosis (AS/ES-AS). Methods: Patients with AS/ES-AS without left ventricular dysfunction were prospectively grouped according to their CPX outcome: 1) peak oxygen-consumption (pVO 2 ) >83% and peak oxygen-pulse (pO 2 pulse) >95% of that predicted; 2) pVO 2 <83% or pO 2 pulse <95% but CPX pointing to other cause than hemodynamic compromise; 3) pVO 2 <83% and respiratory coefficient >1 or clear exercise-limiting discomfort. At baseline Groups 1 (n=77) and 2 (n=35) were handled conservatively and Group 3 (n=18) referred for aortic valve replacement (AVR). Primary end-point was cardiac death, hospitalization with heart failure or AVR with improvement from just pre-AVR to nine months post-AVR in pVO 2 or Physical Component Score from the SF-36 > the estimated clinical relevant difference (5% and 7.5%, respectively). Results: The mean age, valve area and follow-up was 72.1±6.9 years, 0.45±0.11 cm/m 2 and 24±5 months, respectively; 48% were NYHA class ≥II. The end-point was reached in 25.3%, 26.4% and 62.5% in Group 1, 2 and 3, respectively (Group 3 vs. Group 1+2, p=0.007). One patient (0.7%) suffered cardiac death, eight months after recommendation of AVR, and 7 (6.3%) were hospitalized with heart failure. A pO 2 pulse <100% of that predicted was the single predictor of the end-point, odds-ratio 2.55 (95% CI:1.18;5.54) (Table 1). Conclusions: CPX appears useful to separate those with a high probability of improvement with AVR from those, including patients with decreased pVO 2 , with a low event-rate with a conservative approach.