OBJECTIVES: To assess the predictive value of pre-discharge heart rate variability (HRV) parameters in patients with acute coronary syndrome (ACS) treated by percutaneous coronary intervention (PCI). METHODS: 145 consecutive male patients with ACS (aged 57.12 +/- 10.81 years) were included in this study. Fifteen minutes electrocardiogram recording was done to measure time-domain [standard deviation of N-N intervals (SDNN), root-mean square differences of successive R-R intervals (rMSSD)] and frequency-domain [low-frequency (LF) power, high-frequency (HF) power and total power (TP)] HRV parameters before and after PCI. The primary end point was the occurrence of major clinical events (MCE) defined as death, sudden death or re-acute myocardial infarction at the end of 3 months follow-up. RESULTS: At a follow-up of 3 months, MCE occurred in 06 patients (4.14%) (Cardiac death was 3.01%, while that of sudden death was 1.13%). Out of six-MCE, four deaths and two re-AMIs occurred. Pre-discharge HRV values (SDNN, rMSSD, TP, LF and HF) were significantly lower in patients with ACS without MCE. Only total power HRV index (AUC=0.748; p=0.040) showed greater prognostic accuracy. CONCLUSIONS: In conclusion, study showed an increase in SDNN, rMSSD, LF, HF and TP after successful revascularization with PCI in patients who had MCE. The resultant sensitivity, specificity of HRV is still limited in the present study. Particularly, its sensitivity is higher (33-83%) with a modest specificity (61-72%).