Optimal reduction in pulmonary vascular resistance caused by chronic pulmonary embolism is obtained by bilateral pulmonary thromboendarterectomy with removal of occlusive material in all bronchopulmonary segmental arteries that are partially or completely obstructed. The most effective way to obtain this goal is the use of median sternotomy with cardiopulmonary bypass, deep hypothermia, and intermittent periods of circulatory arrest. During circulatory arrest, thromboendarterectomy is performed by specially designed dissectors that allow simultaneous dissection and removal of blood from the surgical field. The operative mortality rate for pulmonary thromboendarterectomy at the University of California, San Diego, between 1990 and 1998 was 9.2% in 1,049 patients.