To determine the immediate and long-term effect of mitral balloon valvotomy (MBV) on left ventricular (LV) volume and function, we studied 17 patients (mean age 27 +/- 9 years) with severe mitral stenosis undergoing MBV by cardiac catheterization and angiography before and immediately after MBV and at mean 12 months later. At baseline, LV end-diastolic volume index (EDVI) was reduced. Ten patients had EDVI < or = 55 ml/m2, and four patients (23.5%) had LV ejection fraction < 50%. EDVI increased from 60 +/- 17 ml/m2 to 66 +/- 17 ml/m2 (p < 0.05) immediately after MBV and increased further to 72 +/- 16 ml/m2 (p < 0.05) later. Stroke volume index increased from 34 +/- 10 ml/m2 to 41 +/- 12 ml/m2 (p < 0.05) immediately after MBV and increased further to 50 +/- 11 ml/m2 (p < 0.001) later. LV end diastolic pressure increased from 12 +/- 5 mm HG to 16 +/- 4 mm HG (p < 0.05) immediately after MBV and fell to 13 +/- Hg at follow-up. LV ejection fraction increased from 57 +/- 7% to 62 +/- 6% (p < 0.05) immediately after MBV and 71 +/- 8% later (p < 0.001). Mean systolic ejection rate increased from 82 +/- 35 ml/sec to 101 +/- 48 ml/sec (p < 0.05) immediately after and 165 +/- 81 ml/sec later (p < 0.05). Systemic vascular resistance fell from 1887 +/- 525 dyne/sec/cm-5 to 1280 +/- 231 dyne/sec/cm-5 (p < 0.001) at follow-up. We conclude that the LV end-diastolic volume and systolic function are reduced in patients with mitral stenosis, and the LV end-diastolic volume is increased immediately after MBV and continues to increase at follow-up 12 months later; the LV ejection performance improves after successful MBV because of an increase in end-diastolic LV volume (preload) and reduction of SVR.