ObjectiveTo evaluate partial occlusion in patients with pulmonary hypertension with regard to a) the degree to which it leads to overestimation of pulmonary artery occlusion pressure (Ppao) and b) identification of factors that could enhance its recognition.DesignObservational descriptive study.SettingMedical intensive care unit.PatientsFourteen patients with pulmonary hypertension and an increased pulmonary artery diastolic pressure (Ppad) − Ppao gradient (≥10 mm Hg).InterventionsNone.Measurements and Main ResultsThe Ppao was recorded during partial occlusion (partial Ppao) and after catheter repositioning to obtain a lower, more accurate value (best Ppao). The error due to partial occlusion, defined as the difference between the partial Ppao and the best Ppao, was 13 ± 5 mm Hg (range, 6–21 mm Hg). The previously widened Ppad − Ppao gradient invariably narrowed during partial occlusion and then increased by 13 ± 5 mm Hg (range, 5–23) during the best Ppao measurement. There was a moderate correlation between the error due to partial occlusion (partial Ppao − best Ppao) and both the mean pulmonary artery pressure (r = .77,p< .01) and the Ppad − Ppao gradient (r = .79,p< .01).ConclusionsPartial occlusion in patients with pulmonary hypertension may lead to significant overestimation of the Ppao and should be suspected when there is a substantial increase in the Ppao without a concomitant increase in the Ppad, as reflected by a marked narrowing of a previously widened Ppad − Ppao gradient.