Subjects receiving an approved ERA or an approved PDE-5 inhibitor must have been on a stable dose for 30 days prior to Baseline, and were willing to remain on a PDE-5 inhibitor or an ERA and at the same dose for the duration of the 12-week Treatment Phase. If a subject chose to discontinue their PDE-5 or ERA prior to entering this study, they must have had a ≥30 day washout period between the last dose of the PDE-5 or ERA and start of the screening phase.