Lung volume reduction surgery (LVRS) can improve the functional capacity of selected patients with severe emphysema. Hypothesized physiologic effects of LVRS include an improvement in right ventricular function, although this has not been investigated in detail. To help clarify this issue, we used fast-thermistor thermodilution at rest and during submaximal upright exercise in 12 patients, before and 6 mo after bilateral LVRS. Preoperatively, all patients had severe airflow obstruction, with a mean FFV1 of 0.69 L and an RV-to-TLC ratio of 0.67. Six months after LVRS, significant improvements occurred in respiratory function measures (+0.39 L in FEV1, p < 0.002; and -0.15 in RV/TLC ratio, p < 0.002) and in right ventricular function indexes measured at rest (+0.21 L in cardiac index [Cl], p < 0.01; and +3.0 ml in stroke volume, p < 0.01) and during exercise (+0.9 L in CI, p < 0.002; +10.0 ml in stroke volume index, p < 0.002; and +20% in ejection fraction [EF], p 0.002). A significant correlation was found between pre- topost-operative changes in the FF response to exercise and changes in the RV/TLC ratio (R = -0.68; p = 0.01). We conclude that a significant improvement in right ventricular performance, particularly during exercise, can occur 6 mo after bilateral LVRS.