This study investigates the influence of postural change on time-domain heart rate variability (HRV) through electrocardiogram (ECG)-based assessment. HRV is a key physiological marker of autonomic nervous system (ANS) activity, and autonomic modulation is strongly influenced by postural change. The one group of subjects underwent ECG monitoring in the supine, sitting, and standing postures, and HRV parameters like mean RR interval, SDNN, RMSSD, and percentage of adjacent NN intervals that differed by more than 50 ms (pNN50) were recorded. The findings indicate significant reductions in HRV parameters with postural tilt, suggesting increased sympathetic dominance. These findings highlight the importance of posture factors in HRV analysis and their contribution to clinical autonomic assessment.