To determine the effect of medical treatment versus lung volume reduction surgery (LVRS) on pulmonary hemodynamics. Three clinical centers of the National Emphysema Treatment Trial (NETT) screened patients for additional inclusion into a cardiovascular (CV) substudy. Demographics were determined, and lung function testing, six-minute-walk distance, and maximum cardiopulmonary exercise testing were done at baseline and 6 months after medical therapy or LVRS. CV substudy patients underwent right heart catheterization at rest prerandomization (baseline) and 6 months after treatment. A total of 110 of the 163 patients evaluated for the CV substudy were randomized in NETT (53 were ineligible), 54 to medical treatment and 56 to LVRS. Fifty-five of these patients had both baseline and repeat right heart catheterization 6 months postrandomization. Baseline demographics and lung function data revealed CV substudy patients to be similar to the remaining 1,163 randomized NETT patients in terms of age, sex, FEV(1), residual volume, diffusion capacity of carbon monoxide, Pa(O(2)), Pa(CO(2)), and six-minute-walk distance. CV substudy patients had moderate pulmonary hypertension at rest (Ppa, 24.8 +/- 4.9 mm Hg); baseline hemodynamic measurements were similar across groups. Changes from baseline pressures to 6 months post-treatment were similar across treatment groups, except for a smaller change in pulmonary capillary wedge pressure at end-expiration post-LVRS compared with medical treatment (-1.8 vs. 3.5 mm Hg, p = 0.04). In comparison to medical therapy, LVRS was not associated with an increase in pulmonary artery pressures.