Background: It has been proved that there is an inspiratory muscle dysfunction in mitral stenosis; Although its causes still remain unknown. Aim: to evaluate the effect of percutaneous balloon mitral valvuloplasty (PMV) on inspiratory muscle performance (IMP) in patients with mitral stenosis (mitral area < 1.5 cm²). Patients and methods: We studied IMP in 8 patients (35 ± 10 years) before and 3 months after successful PMV. Inspiratory muscle strength was studied by measuring maximal statistical inspiratory mouth pressure (MIP). Endurance was evaluated using a two minute incremental threshold loading test in order to obtain the maximal sustainable inspiratory pressure (SIP), with the maximal sustainable load (MSL) the patients could sustain for 2 minutes. Results: Mitral valvuloplasty increased mean cardiac index from 3.1 ± 0.3 to 4.15 ± 0.3 l/min/m² (p<0.01), and significantly decreased mean pulmonary and capillary pressures. The MIP value(118 ± 6 cmH2O), similar to that of normal group, increased to 137 ± 7 cmH2O (p<0.01). SIP and maximal sustainable load were 52 ± 3 cmH2O and 294 ± 29 g respectively, lower than normal subjects (p<0.05) They increased after PMV to 80 ± 3 cmH2O and 463 ± 26 g respectively (p<0.001). Conclusions: PMV improved inspiratory muscle function in patients with severe mitral stenosis, probably secondary to a decrease work of breath and improvement of ventricular function. (Rev Méd Chile 2000; 128: 467-74)