ongoing trials trial from www.clinicaltrials.gov Sildenafil Exercise: Role of PDE5 Inhibition - Phase 2|Phase 3 - Not yet recruiting Year: 2019 Date: September 2019 Author: National Jewish Health|Augusta University|Cystic Fibrosis Foundation Source https://ClinicalTrials.gov/show/NCT04039087 Study design (if review, criteria of inclusion for studies) Interventional - Allocation: Randomized|Intervention Model: Parallel Assignment|Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)|Primary Purpose: Supportive Care Participants Cystic Fibrosis - 9 Years and older (Child, Adult, Older Adult) Interventions Drug: Sildenafil 40mg oral capsule|Drug: Placebo Oral capsule Outcome measures 6 Minute Walk Distance (6MWD)|CFQ-R respiratory domain score|V02 max|Work rate