In an earlier study, sildenafil citrate administered to patients of PAH led to improvement in pulmonary arterial pressure, cardiac output, quality of life, and other parameters as compared to placebo. This protocol provides mechanism for patients who have clinical deterioration on other PAH approved therapies to have access to sildenafil prior to marketing authorization in India.

Inclusion Criteria:

• Subject who complete the A1481244 study and require Sildenafil (Revatio TM) 20 mg TID therapy.
• All women of childbearing potential must use adequate contraception throughout the study and four weeks after completion of the study

Exclusion Criteria:

• Pregnant or lactating women
• Participation in other studies during study participation
• Other severe acute or chronic medical or psychiatric condition or laboratory abnormality that may increase the risk associated with study participation