Objective To investigate whether the extent of preoperative left ventricular （LV） remodeling， indexed by LV end-systolic dimension （LVESD）， influences the recovery trajectory of LV ejection fraction （LVEF） and long-term prognosis following mitral valve surgery in patients with moderate-to-severe mitral regurgitation （MR）. Methods A total of 157 patients undergoing mitral valve surgery for moderate-to-severe MR between January 2020 and December 2024 were prospectively enrolled. Participants were stratified into quartiles （Q1 - Q4） based on preoperative LVESD. The primary outcome was the longitudinal trajectory of LVEF assessed at pre-discharge， 3 months， and 6 months postoperatively， analyzed using linear mixed-effects models. The secondary outcome was a composite endpoint of heart failure rehospitalization or all-cause mortality， evaluated by Cox proportional hazards regression. Results CCompared with the Q1 group， patients in the Q4 group exhibited significantly lower preoperative LVEF and higher NT-proBNP levels （P 0.05）. LVEF improved significantly over time across the cohort （time effect， P 0.001）； however， the Q4 group demonstrated consistently lower LVEF than Q1 at all postoperative timepoints （group effect， P 0.001）， with a modest attenuation of between-group differences over time （time × group interaction， P = 0.008）. After multivariable adjustment， LVEF in the Q4 group remained 13.10， 12.28， and 12.03 percentage points lower than in Q1 at pre-discharge， 3 months， and 6 months， respectively （all P 0.001）. The cumulative incidence of the composite endpoint was significantly higher in Q4 （30.0%） versus Q1 （5.1%， log-rank P = 0.016）. Multivariable Cox analysis identified Q4 membership as an independent predictor of adverse outcomes （adjusted HR = 2.39， 95% CI： 1.11 ? 5.13， P = 0.026）， with a significant dose?response relationship across LVESD quartiles （P for trend = 0.018）. Sensitivity analyses using LVESD ≥ 40 mm as a binary cutoff or modeling LVESD as a continuous variable yielded consistent results. Conclusions Preoperative LVESD， as a marker of LV remodeling severity， independently predicts both the trajectory of early- to mid-term LVEF recovery and adverse clinical outcomes after mitral valve surgery for MR. Although patients with advanced remodeling （higher LVESD） exhibit postoperative LVEF improvement， their absolute recovery remains suboptimal， and they face substantially elevated risks of heart failure rehospitalization or mortality. These findings support earlier surgical intervention before irreversible LV dilation occurs.