Abstract A cohort of patients with breast cancer HER2 positive are exposed to chemotherapy with cardiotoxic drugs like anthracyclines (A) and trastuzumab (T). The decrease in longitudinal strain is a helpful tool to predict clinical cardiotoxicity. The purpose of this paper is to determine if echocardiographic parameters like longitudinal strain with speckle tracking predict subclinical cardiotoxicity compared to conventional echocardiographic parameters. This was a retrospective, observational cohort study that involved 20 patients with breast cancer HER2+ who were treated with a chemotherapy reverse sequence (TH-A). We made a basal echocardiogram, 3, 6, 9 and 12 months after chemotherapy with a cumulative dose of 240mg/m2 of doxorrubicin. Cardiotoxicity was defined as a decrease in left ventricular ejection fraction of 10% below 53%, and subclinical cardiotoxicity as a decline of >15% of longitudinal strain. 5 patients (25%) developed decline in longitudinal strain (subclinical cardiotoxicity) 3 months after initiation of chemotherapy, despite 2 of them had normal LVEF (p = 0.01), with the use of heart failure medication they showed partial reversibility. Lineal regression analysis showed that patients with GLS >-19% at baseline did not present cardiotoxicity during the follow up (p = 0.03). Changes in GLS were independent of left ventricular mass, E/A and peak s’ wave velocity (p = 0.01). The diagnosis of subclinical cardiotoxicity by the decrease of GLS is a useful tool with possible therapeutic implications and possible reversibility of cardiotoxicity in patients with reverse chemotherapy sequence. Significant results Binary analysis of echocardiographic variables Value LVEF p GLS p Basal 62.4 ± 6.7 -19.8 ± 1.8 3 months 59.4 ± 11.1 0.615 -18.1 ± 3.9 0.01 6 months 60.2 ± 8.7 0.354 -18.9 ± 3.3 0.185 9 months 61.6 ± 6.0 0.862 -19.65± 1.9 0.408 12 months 61.1 ± 5.7 0.379 -19.8 ± 1.9 0.859 Binary analysis of echocardiographic variables Abstract P1773 Figure. Sequence of chemotherapy