Reduced cardiopulmonary reserve following extensive pulmonary resection is an everincreasing problem. In certain patients, notably those in the older age group, the cardiorespiratory system is unable to compensate adequately after pneumonectomy and death sometimes occurs in the early postoperative period.1,2 Other patients undergoing extensive pulmonary resection are able to compensate sufficiently for the immediate effects of the sudden reduction in pulmonary parenchyma, only to develop incapacitating symptoms at a later time. Frequently these patients are entirely asymptomatic at rest, only to experience severe dyspnea on slight exertion. These "late" effects are not readily attributable to a lack of functioning lung tissue but are more likely due to a pulmonary vascular insufficiency associated with pulmonary arterial hypertension. Observations on a group of patients 5 to 15 years after pneumonectomy revealed a close correlation between the degree of incapacity and the degree of pulmonary hypertension. The resting pulmonary artery pressures ranged