 The objective of this study is to assess the safety, performance and initial effectiveness of the TIVUSTM System when used for pulmonary artery denervation through subjective and objective change in clinical parameters and haemodynamic evaluation. This is a prospective, multi-center, non-randomized, open-label clinical trail. The study will be conducted in up to 4 centers and will recruit up to 15 patients diagnosed with PAH, functional class III who have stable PAH on a stable drug regimen of two pulmonary arterial hypertension specific medications. 