Previous studies using heart rate variability (HRV) have confirmed decreased HRV in cigarette smokers compared with non smokers. However only few studies have been done considering the effect of smoking on HRV in moderate and severe smokers assessed by pack years. Objective: The main objective of this study was to compare the autonomic functions in male moderate and heavy cigarette smokers.The present was conducted in our department of Physiology. Permission to conduct the study was obtained from Institutional research ethical committee. This study was conducted among male cigarette smokers with age between 20 to 50 years who were apparently healthy. The study group subjects were divided into moderate and heavy smokers considering both the amount and duration of smoking calculated by pack years. HRV data was recorded, statistical analysis was done by independent sample t test to compare between the groups. A p value of <0.05 was considered as statistically significant whereas a p value <0.001 was considered as highly significant.The HRV parameters namely Low frequency (LF) component, LF power expressed in normalized unit (LFnu) and LF-HF ratio were significantly higher in heavy smokers compared to moderate smokers. Total power, high frequency (HF) component and HF power expressed in normalized unit (HFnu) were found significantly less in heavy smokers compared to moderate smokers. Autonomic imbalance characterized by increased sympathetic function with associated decrease in the cardiac vagal modulation was seen in heavy smokers compared to moderate smokers.