Abstract：Objective To investigate the risk factors associated with long-term heart failure in patients undergoing postoperative radiotherapy and chemoradiotherapy for breast cancer. Methods A retrospective case-control study enrolled 117 patients who underwent postoperative radiotherapy and chemoradiotherapy for breast cancer at the Xing’an League People’s Hospital  between March 2015 and December 2022. Based on the occurrence of heart failure during a 5-year follow-up period, patients were divided into a heart failure group （n=35）and a control group （n=82）. Baseline clinical characteristics were compared between the two groups, and univariate and multivariate Cox regression analyses were performed to identified risk factors associated with the development for heart failure. Results Compared with the control group, patients in the heart failure group had a higher mean age, higher mean cardiac radiation dose, larger cardiac irradiated volume, higher prevalence of hypertension, lower hemoglobin levels, lower proportion of normal performance status （PS＝0）, and a higher proportion of targeted therapy use. The differences between the groups were statistically significant （t＝2.015, 3.412, 2.785; χ2＝1.088, 10.482, 4.664, 3.813; all P＜0.05）. Multivariate Cox regression analysis of the above significant variables showed that age（HR＝2.115, 95%CI：1.107～4.041, P＝0.023）, mean cardiac radiation dose（HR＝2.922, 95%CI：1.361～6.273, P＝0.006）, and irradiated cardiac volume（HR＝1.734, 95%CI：1.130～2.816, P＝0.025）were the independent risk factors for heart failure.  Conclusion Patients with breast cancer undergoing postoperative radiotherapy and chemotherapy are at increased risk of developing heart failure after an average of （4.5±3.2） years, along with a higher incidence of adverse cardiovascular events. Advanced age, higher mean cardiac radiation dose, and larger cardiac irradiated volume are the principal risk factors for heart failure.