OBJECTIVE: To assess the effects of trimetazidine (TMZ) added to conventional drug therapy on cardiac autonomic nervous CANS in patients with coronary heart disease (CHD) after the percutaneous coronary intervention (PCI). STUDY DESIGN: Descriptive study. PLACE AND DURATION OF STUDY: Department of Cardiology, The Second Hospital of Hebei Medical University, Hebei, China, from May 2018 to September 2019. METHODOLOGY: The study included 50 patients with CHD after a successful PCI who received trimetazidine plus conventional therapy were included as cases (exposed group), and 50 matched patients were identified as controls (non-exposed group). Heart rate (HR) and heart rate variability (HRV) parameters including sympathetic activity (SDNN, LF), parasympathetic activity (RMSSD, pNN50, SDSD, HF), and sympathovagal balance (LF/HF ratio) were used to evaluate CANS function. RESULTS: There were no statistical differences in the HR and HRV parameters before and after PCI (p>0.05). In the non-exposed group, conventional therapy significantly improved the HRV parameters (all p<0.05), while not affecting HR (p>0.05). In the exposed group, all HRV parameters except HR were improved after 4 weeks of treatment. After 4 weeks of treatment, the exposed group had higher parasympathetic-nerve activity, lower sympathetic-nerve activity, and LF/HF ratio compared to the non-exposed group (all p<0.05). CONCLUSIONS: The application of TMZ based on conventional therapy effectively improved the CANS in CHD patients who underwent PCI. KEY WORDS: Coronary heart disease, Percutaneous coronary intervention, Trimetazidine, Cardiac autonomic nervous system, Heart rate variability.