Background: Heart rate variability (HRV), generated from an electrocardiogram (ECG), can be used to evaluate the autonomic nervous system (ANS). Heart rate changes during different physical activities are due to changing involuntary regulation. Objective: The main aim of the current study is to explore the ANS by analyzing linear HRV parameters, so that clinicians can preliminarily explore ANS function using ECG analysis with their patients. Patients and methods: A total of 15 student volunteers were recorded. Data was collected for 5 minutes for each supine and standing position. The R-peak obtained from an ECG is used to assess the RR-peak, which is also required for HRV analysis. Linear HRV parameters with different time-domain indices and frequency-domain indices are interpreted in 2 body positions. Results: We discovered that the RR interval is longer in the supine position than in the standing position (952.8±181.6 vs. 771.9±164, respectively; P<0.05), and that in comparison to supine position, when standing as opposed to when lying down, the heart rate is higher (81.7±10.2 vs. 65.8±9.1, respectively; P<0.05), where the body is more relaxed. This affects ANS, and stress index values, which are low before increasing in the standing position, starting in the supine position (5.7±2.4 vs. 9.5±2.7, respectively; P<0.05). Conclusion: We conclude that there is a relationship between HRV and the sympathetic system in different positions, where when moving from supine to standing, the values of HRV changes (increases) and, therefore, the stress index changes (increase) and, from this, we note the change (value increase) in ANS.