Introduction: Mitral annular disjunction (MAD) is a structural abnormality characterized by the systolic detachment of the posterior mitral annulus and the ventricular myocardium. It is usually observed coexistent with mitral valve prolapse(MVP) and associated with a mechanical dysfunction despite preserved electrical isolation function of the mitral annulus. Diagnosis depends on the detection of disjunction by imaging modalities as transthoracic echocardiography or cardiac magnetic resonance imaging (CMRI). This study aimed to evaluate left ventricular (LV) function using speckle tracking echocardiography in MVP patients with MAD. Methods: This study was designed as a prospective, single-center study including 103 patients with MVP and 40 age- and sex-matched control subjects. Transthoracic echocardiography and cardiac magnetic resonance imaging were performed to assess LV function and MAD presence. Results: MAD (+) MVP (n=34), MAD (-) MVP (n=69), and control (n=40) groups were enrolled in the study. Among the MVP patients, 34 (33%) had MAD. T negativity in the inferior leads on electrocardiography was more frequent in the MAD (+) group than in the MAD (-) patients (4.3% vs 20.6%, p=0.014). Mitral regurgitation degree, Pickelhaube sign (17.6% vs. 1.4%, p=0.005), and late gadolinium enhancement frequency (35.3% vs. 10.6%, p=0.002) were significantly higher in MAD (+) patients. MAD (+) patients had significantly impaired global longitudinal strain (GLS) -23.1±2.1 vs. -23.5±2.3, P<0.001), basal longitudinal strain (BLS) (-19.6±1.5 vs -20.5±1.9, P < 0.001), and Mid-Ventricular Longitudinal Strain(MVLS) (-22.2±1.7 vs -23.2±2.2, P<0.001) when compared to MAD (-) MVP patients, despite similar LV ejection fraction. All these values of MVP patients were also significantly lower than the control group. The mean MAD distance was 7.8 ± 3.2 mm in MAD (+) patients. Patients with 2 or more symptoms were higher in the MAD (+) group than in the MAD (-) group (4.3% vs 44.1%, P<0.001). Conclusion: This study demonstrated a significant decrease in longitudinal strain in MVP patients with MAD, indicating myocardial dysfunction. These findings suggest that MAD may contribute to LV dysfunction and highlight the importance of early detection in younger patients. Further research is needed to explore the functional implications and long-term outcomes of MAD.