Background In heart failure, the exercise gas exchange Weber (A to D) and ventilatory classifications (VC-1 to VC-4) historically define disease severity and prognosis. However, their applications in the modern heart failure population of any left ventricular ejection fraction combined with hemodynamics are undefined. We aimed at revisiting and implementing these classifications by cardiopulmonary exercise testing imaging. Methods and Results 269 patients with heart failure with reduced (n=105), mid-range (n=88) and preserved (n=76) ejection fraction underwent cardiopulmonary exercise testing imaging, primarily assessing the cardiac output (CO), mitral regurgitation, and mean pulmonary arterial pressure (mPAP)/CO slope. Within both classes, a progressively lower exercise CO, higher mPAP/CO slopes, and mitral regurgitation (<0.01 all) were observed. After adjustment for age and sex, Cox proportional hazard regression analyses showed that Weber (hazard ratio [HR], 2.9; 95% CI, 1.8-4.7; <0.001) and ventilatory classes (HR, 1.4; 95% CI, 1.1-2.0; =0.017) were independently associated with outcome. The best stratification was observed when combining Weber (A/B or C/D) with severe ventilation inefficiency (VC-4) (HR, 2.7; 95% CI, 1.6-4.8; <0.001). At multivariable analysis the best hemodynamic determinants of peak oxygen consumption and ventilation to carbon dioxide production slope were CO (β-coefficient, 0.72±0.16; <0.001) and mPAP/CO slope (β-coefficient, 0.72±0.16; <0.001), respectively. Conclusions In the contemporary heart failure population, the Weber and ventilatory classifications maintain their prognostic ability, especially when combined. Exercise CO and mPAP/CO slope are the best predictors of peak oxygen consumption and ventilation to carbon dioxide production slope classifications representing the main targets of interventions to impact functional class and, likely, event rate.