BACKGROUND It remains unclear whether the current arbitrary screening recommendations of trastuzumab-related cardiotoxicity provides an adequate balance between preventing heart damage and curtailing a curative treatment. AIM To determine the incidence rate and consequences of trastuzumab-induced cardiotoxicity as adjuvant treatment in a real-world scenario. METHODS We present a retrospective analysis of cardiac function measured by echocardiogram at baseline and every 3 mo during trastuzumab treatment. Cardiotoxicity was defined as a drop in left ventricular ejection fraction (LVEF) ≥ 10% from baseline and/or any drop < 50%. RESULTS Between January 2011 and December 2014, 407 patients were selected. Most (93.6%) were treated with an anthracycline followed by a taxane-based regimen and trastuzumab for 12 mo. Forty patients (9.8%) had cardiotoxicity. None of them were symptomatic, and 28 (72.5%) completely recovered LVEF. Cardiotoxicity happened early as shown by LVEF measured on echocardiogram 2 to 4 as compared to 5 to 7 (odds ratio = 2.47, 95% confidence interval: 1.09, 5.63, P = 0.024). There were 54 deaths (13.3%) during the 70-mo follow-up period; 1 (0.2%) was attributed to late cardiotoxicity (4 years after treatment). The absence of symptomatic cardiotoxicity during trastuzumab treatment and moreover the early occurrence on the treatment period may translate into a strategy to evaluate less frequently. CONCLUSION We observed a 10% rate of asymptomatic cardiotoxicity, which mirrors the results from the large adjuvant trials. Despite being transient, an LVEF drop led to frequent treatment delays and interruptions. It remains unclear whether LVEF decline is predictive of late cardiotoxicity, and treatment efficacy is compromised.