PURPOSE OF REVIEW: HER2-targeted therapies have led to improved clinical outcomes in early and advanced breast cancer (BC). We review the long-term cardiotoxicity of HER2-targeted therapy in early and advanced BC, our current knowledge of cardiotoxicity of novel HER2-targeted therapies, and propose a cardiac monitoring (CM) strategy for this population. RECENT FINDINGS: Long-term data from studies with HER2-targeted therapy in the adjuvant setting have failed to demonstrate an increase in cardiotoxicity over time, and rates of cardiotoxicity seen with novel HER2 agents remain low. Despite over a decade of experience with HER2-targeted therapy, CM in clinical practice is inconsistent in patients with early BC and almost non-existent in advanced BC. Long-term follow-up of clinical trials with HER2-targeted agents in early and advanced BC has failed to demonstrate increased rates of cardiotoxicity over time, attesting to the long-term safety of this class of drugs for the majority of patients, although the long-term cardiac safety of newer HER2 agents in the non-clinical trial setting is largely unknown. We propose CM incorporating clinical history, cardiac imaging, and biomarkers.