Abstract: The invention relates to pharmaceutical compositions for the treatment of pulmonary arterial hypertension comprising a prostacyclin or a prostacyclin analogue, preferably epoprostenol, and an endothelin receptor antagonist, preferably bosentan. The invention further provides methods for treating a subject suffering from pulmonary arterial hypertension using the compositions of the invention. The concomitant administration of prostacyclin or a prostacyclin analogue and an endothelin receptor antagonist not only increases the efficacy compared to administration of each alone but also reduces the side effects associated with prostacyclin or prostacyclin analogues.