Background: The evaluation of left ventricular dysfunction in patients with severe mitral valve disease is very important for diagnosis, surgical indication and postoperative follow-up assessments. Speckle Tracking provides additional information to conventional echocardiographic parameters. Objective: Research global longitudinal strain by Speckle Tracking in patiens underwent mitral valve surgery at Hanoi Heart Hospital. Subjects and methods: 35 patients underwent mitral valve surgery at Hanoi Heart Hospital from July 2018 to September 2019. This is a prospective, longitudinal follow-up for at least 3 months research. Results: Postoperative myocardial global longitudinal strain of the left ventricular decreased compared to pre-surgery (-19.85 ± 2.24 vs -16.54 ± 3.01; p < 0.001). The global myocardial longitudinal strain of the left ventricular decreased more in the group whose postoperative EF decreased by ≥10% compared with the group whose EF decreased <10% after surgery (-17.73 ± 2.71 versus -15.28 ± 2.85; p. < 0.05). Mean global myocardial longitudinal strain (GLS avg) after surgery has a linear correlation with left ventricular contraction fraction FS after surgery (r = -0.508; p < 0.005), with left ventricular ejection fraction EF after surgery (r = - 0.402; p < 0.05), with ejection fraction EF biplane after surgery with (r = - 0.768; p < 0.001) and global myocardial longitudinal strain (GLS avg) after surgery há a linear correlation with the degree of change in EF after surgery ≥ 10% (r) = 0.601; p < 0.001). Conclusion: Longitudinal LV deformation assessed by speckle tracking is significant in assessing the decline in left ventricular systolic function in patients with mitral valve surgery.