Balloon atrial septostomy 
The presence of a right-left shunt, secondary to congenital cardiac malformation, or a patent foramen oval, among patients with severe PAH, seems to carry a better prognosis [270]. Atrioseptostomy is an artificial communication interauricular to decrease the right heart volume, subjected to a high after load secondary to increased pulmonary resistances [271]. The surgical creation of a right-left shunt decreases right auricular pressure and increases systemic blood flow, later on, reduction in right ventricular wall tension is expected [271]. Thus, in spite of arterial desaturation induced by the shunt, oxygen delivery is improved [271]. Atrioseptostomy has however never been studied in controlled clinical trials. However, several experienced teams reported their data and it seems that immediate mortality is high, reaching 14% during the first week, particularly in the case of severe desaturation and right heart failure [105,271-273]. Among patients who survived, clinical improvement with regression of symptoms and gain of functional capacity can be observed. Atrioseptostomy should only be carried out in centers with significant experience, both in performance of atrioseptostomy and management of PAH patients, especially post interventional. The impact of balloon atrial septostomy on long term survival has not been established in RCTs [271,274].