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Figure 1 Cardiopulmonary exercising testing measurements (A, oxygen uptake [VO₂] kinetics; B, slope of increase in ventilation versus carbon dioxide production [VE/VCO₂ slope]; and C, rate of oxygen uptake increase per work rate [VO₂/WR]) of one patient with moderate congestive heart failure secondary to ischemic cardiomyopathy (age 60 years, left ventricular ejection fraction of 34%, and systolic pulmonary pressure of 38 mm Hg) recorded after placebo and after sildenafil intake. Protocol consisted of 2 min of rest, 2 min of unloaded exercise at 60 rpm (Unl. Exe. ), ramp work rate of 15 W · min^–1 to maximal exercise tolerance, and 6 min of recovery. Oxygen uptake kinetics data were computer-collected as breath-by-breath measurements, interpolated second-by-second, and averaged at 10-s intervals; VE/VCO₂ incremental changes during maximal exercise data are plotted at 20-s intervals; VO₂/WR incremental changes during maximal exercise data are plotted at 20-s intervals.