Background: To evaluate the incidence, severity and outcome of Trastuzumab-induced cardiotoxicity in HER2 positive Uruguayan breast cancer (BC) patients. Methods: Retrospective observational analysis of HER2 positive BC patients who were treated with Trastuzumab (TTZ) from January 2007 to December 2013 at two Uruguayan centers. Cardiac monitoring included physical examination and assessment of left ventricular ejection fraction (LVEF) by echocardiography that was evaluated before TTZ administration and every 12 weeks thereafter during the duration of therapy. Cardiovascular risk factors analyzed were: obesity (BMI ≥ 30 kg/m2), hypertension, diabetes, sedentary lifestyle and high cholesterol. Results: Sixty nine female patients were found in the databases of our institutions. Median age was 48 years (range: 27-73). Stage at diagnosis was as detailed: 19 % EI, 46 % EII, 29 % EIII and 4 % EIV. Eighty nine percent of patients received adjuvant TTZ , 4 % neoadjuvant TTZ and 7 % received it as a palliative therapy. Thirty patients (43, 5%) had at least one cardiovascular risk factors: 26% hypertension, 16% obesity, 9% sedentary lifestyle, and 4% high cholesterol. Median number of TTZ cycles was 15. Cycles were administered every 3 weeks at standard dose. Nineteen patients (27%) developed cardiotoxicity, of whom 12 had a transient suspension because of a reversible fall in LVEF, 2 had a irreversible reduction in LVEF, and 5 had a symptomatic heart failure. Eighty-nine percent of our patients (62 patients) completed treatment and the rest had a definitive suspension due to a irreversible reduction in LVEF or symptomatic heart failure. Most patients that developed cardiotoxicity (15 out of 19) had cardiovascular risk factors and also most of them (16 out of 19) had received anthracyclines before TTZ. Conclusions: Cardiotoxicity incidence was similar to the incidence reported in the literature and when it was present, in most cases was transient, asymptomatic, and reversible.