Left ventriculography (LVG) was performed to assess severity of mitral regurgitation (MR) on a scale of 0-4+ in 157 patients before and immediately after percutaneous mitral balloon valvotomy (PMV). There were 129 women and 28 men aged 51 +/- 1 (range 13-87) yr. With PMV, mitral valve area increased from 0.9 +/- 0.1 cm2 to 2.0 +/- 0.1 cm2 (P less than .0001). Increase in mitral regurgitation (MR) occurred in 69 patients (44%). Patients were divided into two groups based on increase in MR after PMV. Group A (n = 136) had 0-1+ increase in MR. Group B (n = 20) had greater than or equal to 2+ increase in MR after PMV. The only predictor of increase in MR greater than or equal to 2+ was the ratio of effective balloon dilating area to body surface area (EBDA/BSA). EBDA/BSA was 4.0 +/- 0.1 cm2/m2 in Group A vs. 4.37 +/- 0.2 cm2/m2 in Group B (P = .02). Follow-up of patients in Group B showed: Four patients remained NYHA Class III and required mitral valve replacement 4.3 +/- 1.1 (range 5-21) mo after PMV. One patient who had undergone combined aortic and mitral valvotomy died in the hospital of worsening heart failure. One patient died 1 mo later of sepsis related to a dental abscess. Follow-up of the remaining 14 patients at 9.5 +/- 1.1 (range 2-7) mo showed 10 in NYHA Class I and four in NYHA Class II. Eight of 15 patients (53%) who had repeat left ventriculogram at 9.0 +/- 0.8 mo after PMV had a decrease in MR of one grade when compared to LVG immediately after PMV.