Numerous clinical studies have demonstrated the therapeutic benefit of 
trastuzumab in women with breast cancer. However, a small but not insignificant 
proportion of patients have experienced trastuzumab-associated cardiotoxicity 
during these trials. This phenomenon is generally characterized by an 
asymptomatic reduction in left ventricular ejection fraction (LVEF) or, less 
often, congestive heart failure (CHF). Concomitant anthracycline therapy 
significantly increases the risk for cardiotoxicity during trastuzumab 
treatment, and such regimens are therefore not recommended. The cardiac 
dysfunction associated with trastuzumab is most often reversible upon 
discontinuation of treatment and initiation of standard medical therapy for CHF. 
Prior to treatment initiation, a risk-benefit analysis should be performed for 
each individual patient, including a thorough assessment of potential risk 
factors and cardiac function. Cardiac monitoring should be continued throughout 
trastuzumab therapy and the follow-up period, because early recognition of 
trastuzumab-associated cardiac dysfunction can allow effective medical 
intervention. Following the occurrence of asymptomatic LVEF reduction or CHF and 
appropriate medical intervention, reintroduction of trastuzumab may be 
considered in patients following resolution of normal cardiac function, or in 
those for whom the benefit of antitumor therapy outweighs the risk for CHF.