Patients who undergo thromboendarterectomy for relief of chronic, major-vessel thromboembolic pulmonary hypertension (CT-E PH) offer a unique opportunity to evaluate potential resolution of hypertensive lesions in the small, nonelastic pulmonary arteries. Prior studies have demonstrated that, postoperatively, these patients commonly develop new perfusion scan defects. This "vascular steal" phenomenon occurs almost exclusively in lung segments which, preoperatively, were normally perfused by lung scan, were served by segmental arteries normal by pulmonary angiography, and, at surgery, were uninvolved with thrombi by direct inspection. In this study, we explored whether this intriguing "steal" phenomenon resolves over time. Twenty-nine patients who returned at 11 or more months following thromboendarterectomy were reevaluated by perfusion lung scan, repeated right heart catheterization (26 patients), and pulmonary angiography (25 patients). "Steal" of one or more lung segments occurred in 79 percent of patients in postoperative, predischarge perfusion scans. All demonstrated postoperative improvement in pulmonary hemodynamics, which persisted at follow-up. Postoperative "steal" improved in 96 percent of patients and 86 percent of the "stolen" segments. The results suggest that, in CT-E PH, hypertensive lesions in the small, nonelastic pulmonary arteries are responsible for "steal," and that, with relief of pulmonary hypertension, these lesions can resolve. The study also indicates that postoperative "steal" does not connote either new thromboembolic events or a poor hemodynamic result.