BACKGROUND: The mechanisms of pulmonary hypertension(PHT) are usually quite different in acquired disorders of the left side of the heart from those of congenital heart disease. Accordingly, this study was designed to compare pulmonary hemodynamics immediately after cardiopulmonary bypass(CPB) in patients with undergoing repair of atrial(ASD) or ventricular septal defect(VSD) and mitral valve replacement(MVR). METHODS: 49 patients with PHT defined as a resting systolic pulmonary arterial pressure(SPAP) greater than 35 mmHg were studied and were divided preoperatively into two groups; repair of ASD or VSD(Group I, n=18) and MVR(Group II, n=31). Measurements were made after sternotomy and prior to initiation of CPB and upon stabilization following discontinuation of CPB. RESULTS: In group I, SPAP, DPAP and MPAP decreased by 44%, 22% and 35% respectively and pulmonary vascular resistance index(PVRI) decreased by 47% after CPB. In group II, SPAP, DPAP and MPAP revealed 25%, 32% and 29% reduction respectively and PVRI decrease by 39% after CPB. SPAP decreased more significantly after CPB in group I(44% vs 25%, p<0.05). CI increased significantly in group II while decreased in group I. Intraoperative inotropes and vasodilators were used more in group II than in group I(24/31 vs 6/18). CONCLUSIONS: The successful replacement of the valve and patch repair of defect may reduce both PAP and PVRI moderately in patients with PHT.