Objective: To explore the correlation between heart rate variability (HRV), electrocardiogram (ECG) features, and the severity of coronary artery lesions in patients with coronary artery disease (CAD). Methods: A total of 72 elderly patients diagnosed with CAD by coronary angiography were selected as the CAD group. Based on the median Gensini score, they were divided into a mild lesion group (n=40) and a severe lesion group (n=32). Additionally, 30 healthy individuals undergoing physical examination during the same period were selected as the control group. All subjects underwent 24-hour ambulatory ECG monitoring using the Medex ECG system. Time-domain [standard deviation of all NN intervals (SDNN), root mean square difference of adjacent NN intervals (RMSSD)] and frequency-domain [low-frequency power (LF), high-frequency power (HF), LF/HF] HRV indices, as well as conventional ECG characteristics, were analyzed. Differences in these parameters among the groups were compared. Pearson or Spearman correlation analysis was used to examine the correlations between HRV indices, ECG characteristics, and the Gensini score. Results: Compared with the control group, patients in the CAD group showed reductions in SDNN, RMSSD, and HF (P<0.05), while the LF/HF ratio was increased (P<0.05). Moreover, the severe lesion subgroup exhibited lower SDNN, RMSSD, and HF compared to the mild lesion subgroup (P<0.05), and a higher LF/HF ratio than the mild lesion subgroup (P<0.05). The incidences of ST-T changes and complex ventricular premature beats were higher in the CAD group than in the control group (P<0.05), and were more frequent in the severe lesion subgroup than in the mild lesion subgroup (P<0.05). No significant difference was observed in the incidence of atrial premature beats among the three groups (P>0.05). Pearson correlation analysis showed that SDNN, RMSSD, and HF were all negatively correlated with the Gensini score (P <0.05), while the LF/HF ratio was positively correlated with the Gensini score (P<0.05). Spearman rank correlation analysis indicated that both ST-T changes and complex ventricular premature beats were positively correlated with the Gensini score (P<0.05), while atrial premature beats showed no significant correlation with the Gensini score (P>0.05). Conclusion: The HRV and ECG features in CAD patients correlate with the severity of coronary artery lesions and can serve as non-invasive reference indices for assessing the condition.