Background: Cardiotoxicity is a known complication of anthracycline (A) and trastuzumab (T) therapy, but recent data suggests that it may be underreported. An asymptomatic decline in left ventricular ejection fraction (LVEF) may develop over time and no guidelines exist regarding the optimal duration of follow up. This study was performed to determine the incidence of A or T-associated cardiotoxicity in a large breast cancer population and to identify additional risk factors. Methods: We performed a retrospective chart review using the electronic medical record database at Dartmouth-Hitchcock Medical Center to identify patients with an ICD-9 coded diagnosis of breast cancer (174.9) and congestive heart failure (428, 428.0, 428.1, 428.9, 425, 425.9) from 1999 to 2009. A chart review was subsequently performed to identify a cohort who received A and/or T and who subsequently developed cardiotoxicity, defined as a decline in LVEF to ≤50% on echocardiography or MUGA scan. Additional data on co-morbidities was collected. Results: Four hundred and twelve patients were identified with breast cancer and congestive heart failure, 85 of which were treated with A with or without T. Of the 85 patients, 32 were judged to have A or T-associated cardiotoxicity. Seven hundred ninety three patients were treated with A during this 10 year period, resulting in a 4% incidence of heart failure in our A-treated population. The median age of the affected patients was 58 years (range 30-85) with a mean nadir LVEF of 34%. The mean cumulative doxorubicin dose was 261 mg/m² (range 0-560). Common co-morbidities included hypertension (11/32, 34%), dyslipidemia (9/32, 28%) and smoking history (9/32, 28%). Chest wall radiation was administered to 22/32 (69%), with 9/22 (41%) left-sided and 13/22 (59%) right-sided. Heart failure symptoms were documented in 14/32 (44%) patients. Conclusions: The incidence of A and T-related cardiotoxicity at our institution was relatively low. Hypertension, dyslipidemia and smoking history were common but not enough to be classified as risk factors. Over half of the patients were asymptomatic, thus follow up assessment of LVEF in asymptomatic patients after completion of therapy may be warranted.