Background: We previously reported the cardiac safety results and distant disease-free survival (DDFS) on a phase 2 trial of dose-dense (dd) doxorubicin and cyclophosphamide (AC) followed by paclitaxel (T) and trastuzumab (H) in patients with early stage, human epidermal growth factor receptor 2 (HER2)-positive breast cancer. The incidence of congestive heart failure (CHF) was 1.4% both at a median follow-up of 2 and 7 years. Here, we report updated CHF and DDFS rates with longer follow-up. Methods: Patients were enrolled with HER2 overexpressed (immunohistochemistry 3+) or amplified (fluorescent in situ hybridization ratio > 2.0) disease, regardless of size or nodal status, and baseline left ventricular ejection fraction (LVEF) of > 55%. Patients (pts) received dd AC (60/600 mg/m2) q 2 weeks (w) x 4 →T (175 mg/m2) q 2 w x 4 with H (loading dose 4 mg/kg → 2 mg/kg q w during T → 6 mg/kg q 3 w for rest of 1 year); pegfilgrastim was administered after each chemotherapy cycle. LVEF monitoring with multigated acquisition scan occurred at baseline, months 2 (after AC), 6, 9, and 18 (after therapy completion). Results: From January 2005 to November 2005, 70 pts were enrolled; 2 (3%) and 68 (97%) were treated in neoadjuvant and adjuvant settings, respectively. In 68 pts treated in adjuvant setting, 40 (60%) and 27 (40%) had node-positive and node-negative disease, respectively. The median age was 49 years old (range 27-72); 55 (79%) had hormone-receptor positive disease, 11 (16%) had hypertension, and 21 (30%) had left sided radiation. The median baseline LVEF was 68% [range, 55%-81%]). With a median follow-up of 10.9 yrs, there was no additional CHF event. Therefore, the cumulative incidence of CHF remains to be 1.4% (95% confidence interval [95% CI], 1.36%- 7.7%). The 9 and 10 year DDFS rates were 89% (95% CI, 78%-94%) and 87% (95% CI 75%-93%), respectively. Conclusions: Longer follow-up of this study has demonstrated that ddAC →TH is associated with a low risk of CHF and promising DDFS in patients with early-stage HER2-positive breast cancer.