Pulmonary arterial hypertension is defined by a pressure of at least 25 mmHg. Values can reach 50 mmHg in moderate cases and far more in severe cases. Some cases are secondary to cardiopulmonary disease, whereas primary forms can be due to collagen disorders (e.g scleroderma), viral infections (HIV, human herpes virus type 8, etc.). Numerous cases are induced by drugs, such as appetite suppressants. The recent discovery of BMPR2, a dominant gene with weak penetrance, has opened up several interesting possibilities in this setting. Likewise, pathophysiological research has identified a fall in vasodilatory substances and an increase in vasoconstrictive mediators, opening the way to medical treatments that can postpone the need for lung transplantation.