Increased levels of dysfunctional vWF has beendemonstrated in PAH, with loss of high-molecular-weight multimers.52 This was attenuated by exogenous prostacyclin therapy.52 Subsequent studies have shown low and low–normal levels of vWFantigen and activity in PAH.53,54 These results were attributed to an acquiredvon Willebrand syndrome in the context of a ‘high-shear high-flow’circulation. Here, VWF is linked to pulmonary arterial hypertension.