Although exercise tolerance improved with macitentan, the increase was relatively small. At the start of the study the patients could walk an average of 360 metres in six minutes. After six months the patients taking macitentan 10 mg could walk 12.5 metres further.1 As this change may not be a good surrogate for clinical outcomes, it is important that mortality was studied. However, the drug did not have a significant effect on all components of the primary composite outcome. Most of the benefit was due to macitentan 10 mg reducing the proportion of patients with worsening pulmonary arterial hypertension. Deaths from any cause and from pulmonary arterial hypertension were not significantly different from placebo.