The Effect of Additive On-Demand Sildenafil vs. Dextrose Candy on Maximum Exercise Capacity in Pulmonary Arterial Hypertension

Inclusion Criteria: * Signed Informed consent * Age 18 - 80 years (both sexes) * Pulmonary hypertension (PH) class I (PAH) previously diagnosed according to ESC/ERS 2022/2019 guidelines (mPAP ≥ 20 mmHg, PVR ≥ 2 WU, PAWP ≤ 15 mmHg) during diagnostic right-heart catheterization. * Stable condition, on the same PH-medication for \>4 weeks Exclusion Criteria: * Severe resting hypoxia (PaO2 \<7.3 kPa) * Moderate-to-severe chronic obstructive or restrictive pulmonary disease (FEV1 ≤ 60% predicted, FVC ≤ 60% predicted) * Women with known pregnancy or breast feeding * Other clinically significant concomitant disease states (e.g., severe renal or hepatic disease, unstable cardiovascular disease, etc.) * Concurrent medication with: * Nitric oxide donors (molsidomine, nicrorandil, etc.) * Soluble guanylate cyclase stimulators (riociguat) * Potent CYP3A4 inhibitors (azoles, clarithromycin, protease inhibitors) * History of anterior ischemic optic neuropathy or hereditary retinal disease * Participation in another study with investigational drug with potential influence the study data within the 30 days preceding and during the present study. * Known allergies or hypersensitivity to sildenafil 20mg (Revatio 20mg) or dextrose candy (Dextroenergy) including any of its components