Patients with pulmonary hypertension have damaged pulmonary blood vessels and are more likely to form blood clots than healthy people. Anticoagulants do not directly improve the symptoms of pulmonary hypertension, but they may prolong the life of patients by preventing blood clotting in small pulmonary arteries. Studies have shown that anticoagulation in chronic thromboembolic pulmonary hypertension prolongs life expectancy and improves quality of life; studies in small studies of idiopathic pulmonary hypertension have shown that anticoagulation improves quality of life; other benefits of anticoagulation in pulmonary hypertension are not supported by clinical trials.