Following episodes of pulmonary embolism, the presence of thrombi in the pulmonary arteries leads to severe respiratory insufficiency and chronic right heart failure. We have operated upon 16 such patients, nine men and seven women from 23 to 68 years of age. All had severe dyspnea, 14 had chronic cor pulmonale, six had mental disturbances with syncope, and four had severe cardiac failure. The presence of clots was demonstrated by pulmonary angiography, and the permeability of the distal arterial bed was ascertained by selective injection of the bronchial arteries. In all cases but two a lateral thoracotomy was used so that the obstructed arterial branches could be approached distally. The inferior vena cava was always ligated to prevent recurrences. There were six operative deaths, three from cardiac failure, one from acute pulmonary edema, one from hemothorax, and one following a pyothorax. Ten patients are surviving after 6 months to 10 years. One is still limited because of significant pleuropulmonary sequelae. Six are enjoying good results with marked improvement in their functional limitations, a significant drop in the pulmonary artery pressure, and radiological permeability of previously obstructed arteries. Three are excellent condition--completely asymptomatic.