Percutaneous transvenous mitral valvuloplasty using the double-balloon technique has been attempted in 25 patients (mean age 39 +/- 10 years; 17 women, 8 men) with severe, non-calcified (20 patients) or only slightly calcified (5 patients) mitral stenosis. Valvuloplasty was successful in 22 of the 25 patients. The procedure resulted in a marked increase in mitral valve area from 1.0 +/- 0.2 to 1.9 +/- 0.5 cm2 (p < 0.001) whereas the diastolic transmitral gradient decreased from 11 +/- 4 to 4 +/- 2 mm Hg (p < 0.001). Functional classification according to the New York Heart Association improved from 2.4 +/- 0.6 to 1.7 +/- 0.5 (p < 0.001) and physical working capacity increased from 64 +/- 20 to 76 +/- 17% (p < 0.01). In 3 patients the procedure was not successful: cardiac tamponade and ventricular perforation occurred in 1 patient each and in the third valvuloplasty had to be ended because of lack of cooperation. Follow-up examination was performed 24 +/- 17 months after successful valvuloplasty. In all patients an electrocardiogram, an exercise test and an echocardiogram were obtained after 3, 12, 26 and 40 months. Sinus rhythm was found in 13 and atrial fibrillation in 9 patients before valvuloplasty. After the procedure 3 additional patients could be converted into sinus rhythm. Physical exercise capacity did not change during the follow-up. Mitral valve area determined by Doppler-echocardiography increased from 1.0 +/- 0.1 to 1.7 +/- 0.3 cm2 (p < 0.001) after valvuloplasty and decreased slightly to 1.5 +/- 0.2 cm2 (NS) during the follow-up. Left atrial chamber diameter did not change significantly after the procedure (5.2 vs. 5.0 cm). It is concluded that percutaneous mitral valvuloplasty is successful in 88% of all patients with severe, non calcified mitral stenosis. The clinical result seems to be beneficial and almost all patients had a stable follow-up for two years. Several complications during the procedure occurred in two patients (8%).