This article presents a historical review, as well as a detailed discussion of the incidence, current surgical therapy, and prognosis of chronic unresolved pulmonary embolism. In patients with pulmonary hypertension resulting from this condition, the prognosis is very poor if untreated. In general, medical therapy and anticoagulants and other pharmacologic agents have remained ineffective. In selected patients, surgical embolectomy has improved pulmonary artery pressures, hypoxemia, and functional status as well as overall survival.