We attempted balloon angioplasty in 9 children (ages 0.1 to 10 years) with congenital mitral stenosis. All were symptomatic with severe congestive heart failure and failure to thrive. Effective reduction in mitral gradient was initially achieved in 7 patients. For the entire group, mean valve gradient decreased from 14.8 +/- 5.0 to 8.1 +/- 6.7 mm (p = 0.0007) and mean valve area increased from 1.1 +/- 0.5 to 1.8 +/- 0.9 cm2/m2 (p = 0.003). More than mild mitral regurgitation developed in 2 patients but none required surgery for mitral regurgitation. Poor gradient relief followed dilation of valves with unbalanced chordal attachments, with restriction to the valve apparatus as in mitral arcade, and where the obstruction was not purely valvar as it is with a supramitral ring. No strokes, infection or deaths were due to the procedure. Based on these data, balloon angioplasty of congenital mitral stenosis should be considered before mitral valve replacement in younger patients and in those in whom mitral valve replacement would be problematic.