This nationwide population-based study investigated the differences in the risks of major adverse cardiovascular events (MACEs) among patients with hormone receptor-positive early-stage breast cancer undergoing different combinations of adjuvant treatments in Taiwan. Data from the National Health Insurance Research Database (NHIRD) and Taiwan Cancer Registry (TCR) along with the national mortality data were used. Patients who underwent surgery as the first mode of treatment were divided into four groups based on the subsequent adjuvant therapy received: hormone therapy (H), hormone therapy + chemotherapy (CH), hormone therapy + radiotherapy (RH), and hormone therapy + radiotherapy + chemotherapy (CRH) groups. The risks of fatal and nonfatal MACE among the groups were examined using the inverse probability of treatment weighted hazard ratio (IPTW-HR). Adjuvant treatment, age, tumour size, and comorbidities significantly affected the risks of MACEs among the 19,007 patients analysed. For nonfatal MACEs, the IPTW-HR was significantly lower in the CH group compare to the H group (0.704, 95% confidence interval [CI]: 0.516-0.961). No significant differences in the risks for fatal MACE were observed among the four groups. The IPTW-HRs for haemorrhagic stroke in the CH group was 0.424 (95% CI: 0.188-0.957), for congestive heart failure (CHF) in the RH group was 0.260 (95% CI: 0.088-0.762), and for ischaemic heart disease in the CRH group was 0.544 (95% CI: 0.317-0.934). Increase in the adjuvant modality does not necessarily increase the nonfatal or fatal MACE risks. Cardiac health should be monitored even in patients receiving hormone therapy alone.