Background Mitral regurgitation (MR) is a comorbidity of myocardial infarction (MI), which may promote the incidence of adverse cardiovascular clinical events. However, it is not yet completely understood how MR in MI patients is associated with impaired myocardial deformation. Purpose To determine the damaging myocardium effects of MR in MI patients in terms of the global peak strain (PS) and left ventricular (LV) function, and evaluate the independent risk factors impacting LV deformation after MI. Study type Retrospective. Population One hundred eighty-six MI patients (17.7% female) and 84 normal control subjects (27.4% female). Field strength/sequence 3.0T; late gadolinium enhancement sequence, balanced steady-state free precession. Assessment LV function and LV global PS (global radial peak strain [GRPS]; global circumferential peak strain [GCPS]; and global longitudinal peak strain [GLPS]) were compared among normal controls, MI without MR (MR-) and MI with MR (MR+, mild, moderate, severe) patients. Statistical Tests One-way analysis of variance (ANOVA) test, Mann-Whitney U test, Kruskal-Wallis test, and multiple linear regressions were used. A P value <0.05 indicated statistically significant difference (two-tailed). Results The MI (MR+) patients showed significantly lower LV global PS than both MI (MR-) and control groups in three directions (GRPS 16.66 +/- 7.43%; GCPS -11.27 +/- 4.27%; GLPS -7.75 +/- 3.44%), and significantly higher LV end-systolic (128.85 [87.91, 188.01] mL) and end-diastolic volumes (210.29 [164.07, 264.00] mL) and significantly lower LV ejection fraction (38.23 +/- 13.02%). Multiple regression analysis demonstrated that MR was independently associated with LV GCPS (beta = -0.268) and GLPS (beta = -0.320). LV infarct size was an independent indicator of LV GRPS (beta = -0.215) and GCPS (beta = -0.222). LV end-diastolic volume was an independent indicator of LV GRPS (beta = -0.518), GCPS (beta = -0.503), and GLPS (beta = -0.331). Data Conclusion MR may further exacerbate the reduction of LV global peak strains and function. The MR, infarct size, and LV end-diastolic volume can be used as independent association indicators for LV global PS in MI (MR+) patients. Level of Evidence: 4 Technical Efficacy Stage: 2 TOC Category: Chest.