PURPOSE: To find out new subjects that could be useful to select patients between 9 and 12 points, according to Block's Criteria, to mitral balloon valvotomy. METHODS: One hundred and forty patients underwent mitral balloon valvotomy. Among them, 29 (21%) had between 9 and 12 points. These patients were divided into two groups: group A-patients with mitral valve area > or = 1.5cm2, immediately after balloon valvotomy and in the follow-up period; group B-patients with mitral valve area < 1.5cm2 immediately after or during the follow-up period, patients with severe mitral regurgitation after the procedure and patients who died in the follow-up period. All patients were analyzed by echocardiographic relation criteria (ERC): calcification + subvalvar disease/thickness + mobility. Each one was quantified from 1 to 4 points according to the degree of valvular disease. RESULTS: Group A was composed of 17 (51%) and group B 12 (41%) patients. The variables age, sex, previous mitral commissurotomy and atrial fibrillation did not show difference between groups. In group A mitral valve area (cm2) increased from 1.15 +/- 0.25 to 1.97 +/- 0.26 (p < 0.00001) keeping stable during the follow-up period. In group B percutaneous mitral balloon valvotomy resulted in an increase from 1.26 +/- 0.19 to 1.77 +/- 0.16 (p < 0.00001), however, there was an important decrease in the follow-up period to 1.34 +/- 0.15 (p < 0.00001). The ERC showed that all group A patients had a relation < 1. However, in group B, 10 patients (83%), the relation was > or = 1, and in only 2 patients (17%) was < 1 (p < 0.00001). CONCLUSION: The group of patients between 9 and 12 points in the Block's criteria is heterogenic, therefore, each case might be evaluated individually and the echocardiographic relation criteria should be used in order to select these patients to the procedure.