The vagus or “wandering” nerve is the main branch of the parasympathetic nervous system (PNS), innervating most internal organs crucial for health. Activity of the vagus nerve can be non-invasively indexed by heart-rate variability parameters (HRV). Specific HRV parameters predict less all-cause mortality, lower risk of and better prognosis after myocardial infarctions, and better survival in cancer. A non-invasive manner for self-activating the vagus is achieved by performing a slow-paced breathing technique while receiving visual feedback of one’s HRV, called HRV-biofeedback (HRV-B). This article narratively reviews the biological mechanisms underlying the role of vagal activity and vagally mediated HRV in hypertension, diabetes, coronary heart disease (CHD), cancer, pain, and dementia. After searching the literature for HRV-B intervention studies in each condition, we report the effects of HRV-B on clinical outcomes in these health conditions, while evaluating the methodological quality of these studies. Generally, the levels of evidence for the benefits of HRV-B is high in CHD, pain, and hypertension, moderate in cancer, and poor in diabetes and dementia. Limitations and future research directions are discussed.

The autonomic nervous system plays a central role in maintaining physiological homeostasis, with the vagus nerve as a crucial component. Heart rate variability (HRV) is a non‑invasive biomarker of vagal tone and autonomic flexibility. A reduced HRV has been associated with cardiovascular diseases, hypertension, inflammation and mental health disorders. The present narrative review discusses two promising non‑invasive interventions designed to enhance vagal activity: HRV biofeedback (HRV‑B) and the safe and sound protocol (SSP). HRV‑B utilizes paced breathing at an individual's resonance frequency combined with real‑time HRV monitoring to strengthen baroreflex sensitivity, improve autonomic balance, reduce systemic inflammation and enhance emotional regulation. Extensive research supports the efficacy of HRV‑B in improving cardiovascular outcomes, managing hypertension, reducing depressive and anxiety symptoms, and fostering resilience. By contrast, SSP is a relatively newer auditory‑based intervention grounded in the polyvagal theory. It targets the ventral vagal complex through filtered music to promote social engagement, emotional regulation, and parasympathetic activation. Preliminary studies suggest SSP may benefit individuals with autism spectrum disorder, post‑traumatic stress disorder and cardiovascular disease; however, large‑scale controlled trials are needed to validate its clinical efficacy. By bridging cardiovascular, neurological and psychological domains, both HRV‑B and SSP offer innovative non‑invasive strategies for promoting health and resilience. The review highlights the mechanisms, clinical applications, and outcomes associated with each approach, while also discussing current limitations, such as individual variability, adherence challenges, and the need for further research. Future directions include integrating wearable HRV monitoring, AI‑driven adaptive biofeedback, and expanding investigation across diverse populations to optimize clinical protocols. Together, HRV‑B and SSP represent promising avenues for enhancing vagal neuromodulation in both preventive and therapeutic settings.

This chapter focuses on the application of mind–body practices to support the emotional and physical well-being of children and adolescents in healthcare and therapeutic settings. Emphasizing the critical role of self-regulation techniques in fostering resilience, the chapter explores a range of accessible and evidence-based interventions, including diaphragmatic breathing, autogenic training, progressive muscle relaxation, guided imagery, mindfulness-based relaxation, and cognitive strategies. The discussion highlights the unique challenges faced by young individuals dealing with stress, anxiety, and psychosomatic symptoms, offering practical guidance for clinicians and caregivers to implement these techniques effectively. Through age-appropriate adaptations and interactive methods, the chapter aims to equip children and adolescents with lifelong tools for emotional regulation and stress management. By integrating theoretical insights and practical applications, this work contributes to a growing body of knowledge on the importance of fostering mind–body harmony in younger populations.

PEER REVIEW REPORT MANUSCRIPT: _The Undervalued Role of 5‑Minute HRV in Post‑Acute Infection Syndromes: A Commentary_ AUTHOR: Willem Gielen DATE: July 23 2025 (Preprint, CC‑BY 4.0) GENERAL ASSESSMENT This commentary addresses a timely and clinical...