Abstract Myocardial dysfunction are the most concerning cardiovascular complications of cancer therapies with a poor prognosis, so it’s critical to detect subclinical cardiac abnormalities in order to start cardioprotective therapy early or increased surveillance frequency. Global longitudinal strain (GLS) by echocardiography is an excellent tool for assessing regional and global left ventricular (LV) function. Mechanical dispersion (MD) reflects heterogeneous myocardial contraction, evaluated in many cardiopathies. We evaluated subclinical myocardial dysfunction by GLS and MD using 2D Speckle-tracking Echo, in order to established if MD could be a predictor of ventricular dysfunction in the field of Cardiotoxicity (CTX). Were enrolled 42 women with breast cancer chemotherapy-treated and underwent to Echo evaluation during 3- and 6-months follow-up, compared to evaluation performed before starting chemotherapy (T0). Depending on chemotherapy type were identified 2 groups: Anthracyclines ± Taxol treated (group 1) and Anti-HER2 treated (group 2). CTX diagnosis was made according ESC criteria: LVEF < 50%, LVEF decrease >10% or GLS decrease >15% compared to previous check. At three months, 28% patients (p < 0,009) developed CTX and, in this group, MD was significantly increased compared to T0 (64,4ms ± 18,6 vs 43,48ms ± 7.88 p < 0,001). This finding was consistent regardless treatment group: 65,2 ms ± 5,30 (p < 0.0001) in group 1 and 63,14 ms ± 36,40 (p 0.02) in group 2. Also, GLS was significantly changed: in CTX patients decreased of 9% compared to T0 (p 0.02), but this finding was consistent in group 1 in which GLS decreased of 18% (p 0,01), while in group 2 decrease only of 5% and wasn’t statistically significant compared to T0 (p = 0,3). These patients were treated by beta-blockers or ACE-inhibitors. At six months there was a normalization of MD value (47.7 ± 15.97 ms in CTX group) that was not statistically significant compared to T0 (p = 0,2) and we have interpreted as consequence of positive effect induced by cardioprotective therapy. We believe that MD is a predictor of ventricular dysfunction earlier than GLS during Anti-HER2 treatment, so in this field MD could integrates information obtained from GLS about subclinical dysfunction.