BACKGROUND: Recent guidelines redefined exercise pulmonary hypertension as a mean pulmonary artery pressure/cardiac output (mPAP/CO) slope >3 mm Hg·L ⁻¹ ·min ⁻¹ . A peak systolic pulmonary artery pressure >60 mm Hg during exercise has been associated with an increased risk of cardiovascular death, heart failure rehospitalization, and aortic valve replacement in aortic valve stenosis. The prognostic value of the mPAP/CO slope in aortic valve stenosis remains unknown. METHODS: In this prospective cohort study, consecutive patients (n=143; age, 73±11 years) with an aortic valve area ≤1.5 cm ² underwent cardiopulmonary exercise testing with echocardiography. They were subsequently evaluated for the occurrence of cardiovascular events (ie, cardiovascular death, heart failure hospitalization, new-onset atrial fibrillation, and aortic valve replacement) during a follow-up period of 1 year. Findings were externally validated (validation cohort, n=141). RESULTS: One cardiovascular death, 32 aortic valve replacements, 9 new-onset atrial fibrillation episodes, and 4 heart failure hospitalizations occurred in the derivation cohort, whereas 5 cardiovascular deaths, 32 aortic valve replacements, 1 new-onset atrial fibrillation episode, and 10 heart failure hospitalizations were observed in the validation cohort. Peak aortic velocity (odds ratio [OR] per SD, 1.48; P =0.036), indexed left atrial volume (OR per SD, 2.15; P =0.001), E/e’ at rest (OR per SD, 1.61; P =0.012), mPAP/CO slope (OR per SD, 2.01; P =0.002), and age-, sex-, and height-based predicted peak exercise oxygen uptake (OR per SD, 0.59; P =0.007) were independently associated with cardiovascular events at 1 year, whereas peak systolic pulmonary artery pressure was not (OR per SD, 1.28; P =0.219). Peak V o ₂ (percent) and mPAP/CO slope provided incremental prognostic value in addition to indexed left atrial volume and aortic valve area ( P <0.001). These results were confirmed in the validation cohort. CONCLUSIONS: In moderate and severe aortic valve stenosis, mPAP/CO slope and percent-predicted peak V o ₂ were independent predictors of cardiovascular events, whereas peak systolic pulmonary artery pressure was not. In addition to aortic valve area and indexed left atrial volume, percent-predicted peak V o ₂ and mPAP/CO slope cumulatively improved risk stratification.