Pimobendan is a positive inotropic agent that dilates blood vessels and sensitizes the myocardium to calcium. We studied the clinical usefulness of single oral doses of pimobendan (2.5 mg) in 8 patients with pulmonary hypertension caused by chronic pulmonary emphysema. We measured the short-term effects of pimobendan on pulmonary hemodynamics and gas exchange. Pimobendan significantly decreased mean pulmonary artery pressure from 23.4 +/- 3.4 to 18.5 +/- 2.5 mmHg, and total pulmonary resistance from 383 +/- 111 to 281 +/- 81 dyne.sec.cm-5, while oxygen delivery and cardiac output increased significantly (oxygen delivery: from 81.8 +/- 10.2 to 93.5 +/- 16.2 ml O2/min. cardiac output: from 4.98 +/- 0.76 to 5.77 +/- 1.49 l/min, means +/- SD). Systemic vascular resistance was not significantly reduced. The ratio of pulmonary to systemic vascular resistance was reduced, but not significantly. Arterial oxygen tension (PaO2) and arterial carbon dioxide tension (PaCO2) did not change significantly. These results indicate that pimobendan may be useful in the treatment of patients with secondary pulmonary hypertension.