In mitral regurgitation (MR), left atrium (LA) and left ventricle (LV) undergo remodeling even if the patient is asymptomatic. The aim of our study was to identify the best echo index that correlates with MR severity in asymptomatic patients affected by MR. We enrolled 150 MR patients (50: mild, 50: moderate, 50: severe), asymptomatic for exertional dyspnea and 50 healthy controls. MR was graded using Doppler quantitative method. All underwent standard and Speckle Tracking Echocardiography (STE) with analysis of global peak atrial longitudinal strain (PALS), LV longitudinal strain (LS) and global atrio-ventricular strain (GAVS). LA dimensions showed significant differences between the groups while LV end-diastolic diameter did not significantly differ, although having a slight increase. PALS was slightly higher in patients with mild MR, while decreased in moderate and, mainly, in severe MR (controls 37.4 ± 12.2%, mild MR 38.2 ± 9%, moderate MR 29.1 ± 9%, severe MR 19.8 ± 10.6%, p < 0.0001 by ANOVA); the same was found for GAVS (56.1 ± 13%, 57.6 ± 9.7%, 48.2 ± 9% 39 ± 9.4%, p < 0.0001 by ANOVA). LV LS showed a tendency for gradual reduction in the three groups. In multivariate analysis, PALS and GAVS were far superior than GLS as predictors of MR groups. PALS emerged as an added value to the LA indexed volumes as predictor of MR severity. STE-derived PALS and GAVS emerged as promising tools to investigate heart longitudinal function in patients with chronic MR and no symptoms. PALS can represent a surplus in the prediction of severity of MR, in addition to the assessment of LA volumes.