Background The risk of ischemic heart disease (IHD) due to the impact of gonadotropin‐releasing hormone (GnRH) agonists among female patients with breast cancer remains a controversy. Methods Information from the Registry for Catastrophic Illness, the National Health Insurance Research Database (NHIRD), and the Death Registry Database in Taiwan were analyzed. Female patients with breast cancer were selected from the Registry for Catastrophic Illness from January 1, 2000, to December 31, 2018. All the breast cancer patients were followed until new‐onset IHD diagnosis, death, or December 31, 2018. A Kaplan–Meier survival curve was drawn to show the difference between patients treated with and without GnRH agonists. The Cox regression analysis was used to investigate the effects of GnRH agonists and the incidence of IHD. Results A total of 172,850 female patients with breast cancer were recognized with a mean age of 52.6 years. Among them, 6071(3.5%) had received GnRH agonist therapy. Kaplan–Meier survival curves showed a significant difference between patients with and without GnRH therapy (log‐rank p < 0.0001). Patients who received GnRH therapy had a significantly decreased risk of developing IHD than those without GnRH therapy (HR = 0.18; 95% CI = 0.14–0.23). After adjusting for age, treatment, and comorbidity, patients who received GnRH therapy still had a significantly lower risk of developing IHD (AHR = 0.5, 95% CI = 0.39–0.64). Conclusion The study showed that the use of GnRH agonists for breast cancer treatment was significantly associated with a reduced risk of IHD. Further research is required to investigate the possible protective effect of GnRH on IHD. For female patients with breast cancer, the use of GnRH agonists was significantly associated with a reduced risk of IHD. After adjusting for age, treatment, and comorbidity, patients who received GnRH therapy had a significantly lower risk of developing IHD (AHR=0.5, 95% CI=0.39‐0.64). GnRH agonists were significantly associated with a lower risk of incident IHD in all the subgroups, except in those with CKD or COPD, respectively.