Interaction Study in Patients With Pulmonary Hypertension and Stable Treatment of Sildenafil 20 mg TID

Inclusion Criteria: * Patients with pulmonary hypertension stable for the last 6 weeks * Treated with Sildenafil 3 × 20 mg * Undergoing routine invasive diagnostics. Exclusion Criteria: * Pre-existing lung disease other than pulmonary arterial hypertension, * Acute or severe chronic left heart failure, * Severe coronary artery disease, * Uncontrolled arterial hypertension; * Congenital or acquired valvular or myocardial disease except acquired tricuspid valve insufficiency due to pulmonary hypertension, * Systolic blood pressure \< 100 mmHg, heart rate \< 55 bpm or \>105 bpm, PaO2/FiO2 \< 50 mmHg, * PaCO2 \> 55 mmHg, * Severe hepatic insufficiency, * Severe renal insufficiency, * Administration of strong CYP3A4 inhibitors or inductors