Oral anticoagulation 
Pathology specimens from PAH patients may show in situ thrombosis and thrombi recanalisation. Only few studies support anticoagulation treatment in PAH (mostly retrospective or not randomized) [202,203]. Current recommendations propose oral anticoagulation aiming for targeting an International Normalized Ratio (INR) between 1.5 and 2.5. Although the somewhat sparse evidence base is derived exclusively from idiopathic, heritable and PAH due to anorexigens, anticoagulation has been generalised to all patient groups, given the absence of contraindication. Anticoagulation is usually not recommended in porto-pulmonary hypertension because of the risk of esophageal variceal haemorrhage. In patients with systemic sclerosis, oral anticoagulation can be difficult to manage because of their high risk of bleeding, especially from the gastrointestinal tract. Variceal ligation is a preventive option in these cases. Long-term oral anticoagulation is essential in CTEPH with an INR which is recommended to be between 2 and 3.