<p>The left atrium (LA) undergoes significant structural and functional alterations in patients with mitral stenosis (MS) due to increased afterload and pressure overload. percutaneous transvenous mitral commissurotomy (PTMC) is the preferred treatment for severe MS, yet its long-term impact on LA mechanical function remains poorly understood. This study evaluates the intermediate and long-term effects of PTMC on LA function in patients with severe MS and normal sinus rhythm. This prospective, non-randomized, observational study included 53 patients (mean age: 33.3 ± 6.44 years) with severe symptomatic MS who underwent successful PTMC. LA volumes and mechanical function indices, including LA stroke volume (VS), LA ejection fraction (LAEF), LA expansion index (LAEI), LA passive emptying fraction (LAPEF), and LA active emptying fraction (LAAEF), were assessed using two-dimensional echocardiography at baseline, immediately post-PTMC, and at 1, 3, and 5 years. Generalized estimating equations (GEE) were used to analyse temporal trends in LA function. LA reservoir (LAEF, LAEI) and conduit function (LAPEF) showed significant improvement up to 1year post-PTMC, followed by a plateau at 3 and 5 years. LA pump function (LAAEF) demonstrated a delayed but sustained improvement up to 3 years, with no further changes thereafter. Phasic LA volumes (Vmax, Vmin, Vp) decreased significantly up to 1 year, stabilizing over the long term. PTMC leads to significant improvement in LA functional indices, particularly within the first year, followed by stabilization in the long term. These findings suggest that while PTMC induces favourable LA remodeling, certain structural changes may be irreversible. Further research is needed to assess the impact of these functional improvements on long-term clinical outcomes, including AF and mortality.</p>