BACKGROUND: In patients with mitral stenosis, the degree of pulmonary hypertension is expected to be related to the severity of mitral valve obstruction. However, some patients with severe mitral stenosis do not develop reactive pulmonary hypertension. MATERIALS AND METHODS: We evaluated 34 patients with symptomatic mitral stenosis undergoing percutaneous mitral valvuloplasty by clinical, echocardiographic, and invasive hemodynamic(cardiac cathrterization) data. Prevalvuloplasty data were available in 34 subjects[mean age 38+/-9 year ; women 74% ; NYHA class 1 (6 patients), class 2 (17 patients), class 3 (7 patients), class 4 (4 patients) ; in electrocardiography, NSR(23 patients), Atrial fibrillation(11 patients)]. RESULTS: 1) The pulmonary vascular bed gradient was significantly correlated with pulmonary vascular resistance(r=0.91), mean pulmonary artery pressure(r=0.82), transmitral mean pressure gradient(r=0.64) and mitral valve area(r=-0.48). The pulmonary vascular resistance was significantly correlated with mena pulmonary artery pressure(r=0.77), transmiral mean pressure gradient(r=0.61) and mitral valve area(r=-0.54), NYHA functional classification(r=0.36). However, the pulmonary vascular bed gradient and pulmonary vascular resistance was not significantly correlated with age, sex, cardiac output, the severity of mitral regurgitation and mean left atrial pressure. 2) The mean pulmonary artery pressure was significantly correlated with mean left atrial pressure(r=0.80), transmitral mean pressure gradient(r=0.72) and mitral valve area(r=-0.47). 3) When patients were divided into those with a pulmonary vascular bed gradient > 12mmHg and = 12mmHg, the two groups were significantly different for many of these measures-Pulmonary vascular resistance(p=0.004), mean pulmonary artery pressure(p=/p<0.0001), transmitral mean pressure gradient(p=0.008), mitral valve area(p=0.04). 4) The mean left atrial pressure was significantly correlated with mean pulmonary artery pressure but not with pulmonary vascular resistance and pulmonary vascular bed gradient as the index of reactive pulmonary hypertension. 5) Results of multiple regressin analysis of factors affecting pulmonary vascular bed gradient showed that transmitral mean pressure gradient was the most significant factor(op<0.0001). 6) The decrease in mean pulmonary artery pressure from immediate before to immediate after balloon commissurotomy was related to pulmonary vascular resistance(r=0.51), pulmonary vascular bed gradient(r=0.63), mean left atrial pressure(r=0.60), transmitral mean pressure gradient(r=0.50), mitral valve area(r--0.41). CONCLUSION: In patients with mitral stensis, the degree of reactive pulmonary hypertension was significantly related to the severity of mitral stenosis(transmitral mean pressure gradient, mitral valve area) but not to mean left artial pressure. In some patients the degree of mitral stenosis could not expect the development of reactive pulmonary hypertension. It is suggested that specific predictors of pulmonary hypertension on an individual patient cannot be identified based solely on the severity of mitral valve disease and must include many factors associated with pulmonary parenchymal diseases, other heart diseases, and duration of mitral stensis.