This cluster of papers focuses on the analysis, applications, and implications of heart rate variability (HRV) in understanding autonomic nervous system function, physiological time series analysis using entropy methods, neurovisceral integration, its role as a marker of stress and health, and its associations with cardiovascular disease, emotion regulation, and baroreflex sensitivity. The cluster also covers the impact of HRV on various health conditions such as diabetes, depression, anxiety disorders, and mortality prediction.