Pulmonary arterial hypertension (PAH) is a progressive disease that, without treatment, ultimately results in right heart failure and death. For the majority of patients with advanced PAH, therapy requires cumbersome drug delivery devices with serious side effects. Endothelin, a potent endogenous vasoconstrictor, is increased in individuals with PAH. The development of bosentan, a novel, well-tolerated, orally active endothelin antagonist, has significantly changed the therapeutic approach to PAH. Recent clinical trials have demonstrated that treatment with bosentan produces favourable effects on cardiopulmonary haemodynamics, exercise capacity, WHO functional class and time to clinical worsening in PAH.