A large left atrial (LA) v. wave can be observed in patients with pure mitral stenosis (MS) because of decreased LA compliance. Few data are available regarding the relation between the magnitude of the LA v wave and pulmonary artery pressure in MS. We hypothesized that pulmonary artery pressure may be higher in patients with decreased LA compliance and thus a large v. wave. We analyzed the right-sided cardiac and transseptal catheterization data in 113 patients (16 men and 97 women, mean age 39 years) with pure rheumatic MS in sinus rhythm. Peak systolic, diastolic, and mean pulmonary artery pressures were measured with right-sided cardiac catheterization. The magnitude of LA a and v. waves were measured through transseptal catheterization. Two-dimensional and Doppler echocardiography were also performed to measure LA size, mitral valve area, mean mitral gradient, and valvular regurgitation. Multiple regression analysis was performed to identify the most important factor in the determination of pulmonary artery pressure. A large v wave, defined if peak v wave height exceeded the mean LA pressure by > or =10 mm Hg, was observed in 43 of 113 patients (38%). Increased pulmonary artery systolic pressure (> or =50 mm Hg) was observed in 38 patients (34%). Univariate analysis showed that the factors associated with increased pulmonary artery systolic pressure were smaller mitral valve area, higher mean mitral gradient, higher mean LA pressure, and higher LA v. wave; among them, LA v wave (p <0. 001) and mean mitral gradient (p<0.001) were significant independent factors for pulmonary artery systolic pressure in multivariate analysis. In conclusion, in patients with pure MS and sinus rhythm, the magnitude of the LA v. wave is strongly associated with pulmonary artery pressure. This finding may suggest that LA compliance is a major contributing factor determining pulmonary artery pressure in pure MS.