The use of trastuzumab in the adjuvant and metastatic treatment of breast cancer 
is associated with both symptomatic and asymptomatic cardiotoxicity. The 
long-term significance of these events, isolating known cardiotoxic effects of 
anthracyclines from those of trastuzumab, and the appropriateness of referring 
to trastuzumab-related cardiotoxicity as reversible rather than responsive to 
trastuzumab withdrawal and heart failure medical therapy, are issues that 
continue to be debated. This article provides an overview of the available 
cardiac safety data from the major trastuzumab clinical trials in breast cancer, 
highlighting areas of ongoing controversy. Important recent data documenting the 
occurrence and prognostic use of cardiac troponin I elevations among patients 
treated with trastuzumab are placed into context with the mechanistic insight 
these data provide and the implications for clinical practice today.