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

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