Objective: We evaluated regional left atrial (LA) myocardial deformations by strain (S) and strain rate (SR) imaging during LA pump, reservoir, and conduit phases in patients with chronic rheumatic mitral regurgitation (MR). Materials and Methods: This cross-sectional observational study included 42 patients with moderate-to-severe MR who had normal left ventricular (LV) function, and 36 healthy control subjects. Conventional echocardiographic data were used to calculate LV and LA dimensions, volumes and functional indices (LA ejection fraction, LA active and passive emptying fraction). Longitudinal S/SR indices of the mid and superior segments of LA walls were measured during the three LA phases. Student t-test, Mann-Whitney U test, Chi-square test and Bland-Altman analysis were used for statistical analysis. Results: LV systolic functions were similar in the patient and control groups. LV diameters, LA diameters and LA volumes were greater in the patient group compared with the control group (p<0.05, p<0.001, and p<0.001). LA ejection fraction and LA active emptying fraction values were lower in the patient group than in the control group (56±7 vs. 63±5%, 33±9 vs. 40±4%, p<0.05 for both). During the three LA phases, longitudinal S/SR values were significantly lower in all the segments in the patient group compared with the control group (p<0.001 for S, p<0.001 and p<0.05 for SR). Conclusion: Regional LA longitudinal myocardial deformations are observed to be impaired during all the mechanical phases in patients with moderate-to-severe MR. Volume overload, remodeling and rheumatic effects may be responsible for the LA myocardial dysfunction in these patients.