This is a standard-design, double-blind, parallel-group, placebo-controlled trial.

Overall, 72 well-characterized PAH patients, 36 subjects in each treatment group (apabetalone 100 mg BID or matching placebo), that have been stable for >4 months on standard PAH-therapies, as per guidelines (Galie, Humbert et al. 2015) will be recruited in 8-15 participating centres (site selection currently ongoing). The participating centres will be recruited if they have the same approach to PAH patients in terms of choice and timing of treatments, and have expertise in performing trials in PAH. The initial Health Canada approval will be obtained. Apabetalone will be provided by Resverlogix Corp. Canada, but Resverlogix had no input into the trial design and will not be involved in the conduct of the trial, analysis, interpretation of the results or the final manuscript.

A 4-week pre-treatment phase will allow ensuring that patients are on stable doses of PAH medication. Patients will be given apabetalone 100mg BID or placebo.

Patients will be regularly followed to assess whether side effects. At baseline and week 24, a cardiac catheterization will assess changes in pulmonary hemodynamics and RV function.

An end-of-study visit is planned at week 28.