Alongside reversible secondary pulmonary arterial hypertension accompanying neonatal respiratory distress, there are primary PAH leading to the persistence of the foetal circulation. This is a true functional neonatal heart disease which may occur alone or be seen in association with another form of neonatal distress such as respiratory distress secondary to the inhalation of amniotic fluid. Any neonatal hypoxaemia irreductible by classical methods should suggest the possibility of persistent pulmonary arteriolar vasoconstriction and lead, in the absence of systemic hypotension, to the administration of vasodilators. These data remain in the preliminary stage and further studies, in particular pharmacological, of these drugs are necessary.