The purpose of this study is to determine the clinical, functional and hemodynamic response after six months of sildenafil 50 mg TID in patients with pulmonary arterial hypertension.

Pulmonary arterial hypertension is a chronic devastating disease. There are few approval oral treatments. Sildenafil, a phosphodiesterase 5 inhibitors, has been recently approved for patients on functional class II and III showing hemodynamic benefits after 12 weeks of treatment. Long term hemodynamic evaluation after sildenafil treatment has not been evaluating in pulmonary arterial patients on functional class II to IV.

The protocol has been designed to evaluate patients on functional class II to IV from baseline conditions and after 6 months of sildenafil treatment (50 mg po TID). Clinical (functional class), functional (walked distance-6 minute walking test) and Hemodynamic evaluation is planned to be performed at baseline and after 6 months of treatment.

Inclusion Criteria:

• Patients older than 15 years old with Pulmonary arterial hypertension according with WHO hemodynamic definition,
• Who signed informed consent,
• Able to swallow tablets and follow instructions.

Exclusion Criteria:

• Patients with pulmonary hypertension with other categories than pulmonary arterial hypertension (associated to COPD, lund diseases, sleep apnea, thromboembolic disease, hight altitude), patients asymptomatic, patients who were responders to adenosine during hemodynamic test, patients treated with specific treatments for pulmonary arterial hypertension before started the study such as sildenafil, prostanoids, endothelin receptors blockers.