Introduction: obesity is an important public health problem worldwide. It is believed that obese candidates for bariatric surgery present cardiac autonomic dysfunction and that weight reduction achieved through surgical treatment of obesity may promote improvement in autonomic nervous system activity, minimizing cardiovascular risks. Objective: thus, the objective of this study is to assess the impact of surgical bariatric weight reduction on HRV and on anthropometric measurements (BMI, WHtR, and WC) comparing obesity classes II and III. Method: the study included 25 obese individuals who underwent a preoperative assessment. Anthropometric measurements and heart rate varability (HRV) were collected preoperatively. The participants were then divided into two groups: obesity class II and obesity class III (class II: BMI from 35 to 39 k/m2, and class III: BMI from > 40 kg/m2). Thirty days after surgery, a postoperative assessment was performed and the data were compared. Results: our results confirm that both class II and III obesity groups presented altered HRV preoperatively and that the participants in the obesity II group showed a statistically significant increase in the HRV index when compared to the obesity III group, through the mean RR, PNN50, SNS, and stress index. Conclusion: the findings confirmed the important contribution that bariatric surgery makes to improving metabolic health and lowering important obesity indices. The varying alterations in heart rate variability indicate subtle advantages concerning autonomic function, especially for individuals classified as obese II