This is a randomized, double-blind, placebo-controlled, multicenter study. The key measure of effectiveness of the study drug will be determined using a 6-minute walk test. Eligible patients will be treated for 16 weeks and may be eligible to enter a 52-week extension phase study (PHIRST-2). Study procedures for both studies (PHIRST-1 and PHIRST-2) will include routine blood tests, medical history, physical exams, questionnaire responses, and exercise tests.
The purpose of this study is to evaluate the safety and effectiveness of tadalafil for the treatment of pulmonary arterial hypertension.