The study included 106 incident patients from the Swedish Pulmonary Arterial Hypertension Registry, treated with phosphodiesterase-5 inhibitors for ≥90 days, who were not at a pre-specified treatment goal, i.e. in World Health Organisation functional class III, with 6-min walking distance 165–440 m, and N-terminal prohormone of brain natriuretic peptide >300 ng/L. Here, NPPB is linked to pulmonary arterial hypertension.