Limited data are available on long-term cardiac safety of adjuvant anthracycline chemotherapy in breast cancer patients over age 65 years. We evaluated rates and predictors of congestive heart failure (CHF) in this population. We used the Surveillance, Epidemiology, and End Results Medicare database and included women with no history of CHF who were age 66 to 80 years and diagnosed with stage I to III breast cancer from 1992 to 2002. Cumulative rates of CHF were estimated, and multivariable Cox regression analysis was used to determine factors associated with the development of CHF. A total of 43,338 women were included. Anthracycline-treated women were younger, with fewer comorbidities and more advanced disease than women who received nonanthracycline or no chemotherapy (P < .001 for each). The adjusted hazard ratio (HR) for CHF was 1.26 (95% CI, 1.12 to 1.42) for women aged 66 to 70 treated with anthracycline compared with other chemotherapy. For women aged 71 to 80, adjuvant chemotherapy type was not associated with CHF. The following baseline characteristics were significant predictors of CHF: age (HR, 1.79 per 10 years; 95% CI, 1.66 to 1.93), black race (HR, 1.40; 95% CI, 1.30 to 1.50), trastuzumab treatment (HR, 1.46; 95% CI, 1.21 to 1.77), hypertension (HR, 1.45; 95% CI, 1.39 to 1.52), diabetes (HR, 1.74; 95% CI, 1.66 to 1.83), and coronary artery disease (HR, 1.58; 95% CI, 1.39 to 1.79). Left-sided radiotherapy did not confer an elevated risk of CHF (HR, 1.04; 95% CI, 0.98 to 1.11). Women aged 66 to 70 years who received adjuvant anthracyclines had significantly higher rates of CHF. The difference in rates of CHF continued to increase through more than 10 years of follow-up.