Abnormal passive elastic properties occur in patients with severe mitral stenosis and are attributed to either: (i) chamber atrophy due to unloading; (ii) myocardial fibrosis; (iii) right and left ventricular (LV) interaction; or (iv) internal restrictions due to a rigid mitral valve apparatus. This study aimed to evaluate the effect of percutaneous mitral balloon valvuloplasty (PMV) on passive elastic properties in 19 patients with severe mitral stenosis; 10 patients with normal coronary arteries and LV function served as controls. LV high-fidelity pressure measurements and simultaneous biplane LV angiograms were obtained in all patients. The constant of chamber stiffness (b; ml-1) was calculated from the diastolic pressure-volume relationship, and that of myocardial stiffness (?) from the diastolic stress-strain relationship. The time constant of relaxation (T; ms) was calculated from the LV pressure decay during isovolumic relaxation. Regional ejection fraction (EF) was determined in six regions of the right anterior oblique (RAO) and left anterior oblique (LAO) angiographic projections. Mitral valve area increased from 1.0 to 2.2 cm2 after PMV, while diastolic pressure gradient fell from 14 to 4 mmHg. Global LV EF was slightly reduced (57% versus 63%; p <0.05) before PMV and normalized thereafter. Regional EF increased significantly (p <0.05) in the posterolateral region of the LAO projection after intervention. Myocardial stiffness was increased before, and decreased significantly after, PMV (from 16 to 11; p <0.05). Rate of relaxation and chamber stiffness remained unchanged. In conclusion, myocardial stiffness is increased in patients with mitral stenosis but normalized after successful PMV. The improvement in passive elastic properties after PMV can be explained by the mobilization of the subvalvular apparatus with improved regional LV function.