Introduction: heart rate variability is a key indicator of cardiovascular health and autonomic balance, influenced by various factors such as age and stress. Objective: to relate heart rate variability to body composition, physical activity levels, sleep quality, and self-perceived stress in young Chilean adults with low cardiometabolic risk. Methodology: a cross-sectional study was conducted in 2024 with the participation of 32 young adults (18 to 30 years old), selected based on inclusion criteria related to adequate physical activity levels and the absence of chronic diseases. The analysis considered variables such as body composition, sleep quality, stress levels, physical activity levels, and heart rate variability, with the latter measured over a 5-minute resting period. Results: age showed a significant negative relationship with RMSSD (β = -0.43, t = -2.48, p = .02), indicating a decrease in parasympathetic activity as age increases. Self-perceived stress, however, did not show a significant impact on RMSSD (β = .09, p = .60) or the RR/RMSSD ratio (β = -0.37, p = .04). Discussion: the findings highlight the importance of heart rate variability as an indicator of autonomic health, emphasizing how age and stress impact vagal modulation. These results reinforce the need to integrate autonomic monitoring into preventive strategies to improve cardiovascular health. Conclusion: heart rate variability is significantly related to age and self-perceived stress. These findings underline the importance of integrating autonomic monitoring into preventive health strategies.