Introduction: Transtuzumab is a monoclonal antibody and it is administered in HER2-positive breast cancer metastasis. Data from the literature are poor about transtuzumab induced cardiomyopathy evolution and treatment. Methods: We present the case of a patient with dilated cardiomyopathy with severe LV systolic dysfunction treated for breast cancer with transtuzumab, being admitted, assessed, treated and monitored at the Cardiology Clinical Emergency Hospital “Bagdasar Arseni”. Results: Patient, 64 years old, diagnosed with metastatic breast ductal carcinoma, who was operated in 2012, in treatment from January 2013 with transtuzumab, being under transtuzumab treatment, develops grade IV NYHA heart failure and impaired LV systolic function from 50% to 23%. After discontinuing the treatment with transtuzumab and administration of beta-blocker and diuretic, and after clinical status and echocardiographic reevaluation at 2 months, clinical improvement was found, with improvement of systolic LV longitudinal function, but with maintaining severely impaired LV EF. Conclusions: The case requires a multidisciplinary approach with periodic modulation cardiology and oncology treatment according to the evolution.