<p>Understanding the mind–body relationship is increasingly important in healthcare. Dysregulation of the autonomic nervous system (ANS) has been linked to both physical and mental health issues. Heart rate variability biofeedback training (HRVBt), which targets ANS regulation, is gaining popularity and is becoming more portable with advancing technology. While meta-analyses have shown that HRVBt can improve psychological and physiological outcomes, no review has specifically examined portable/remote HRV biofeedback training (P/R-HRVBt). Given the digital transformation of healthcare, this review aimed to evaluate the feasibility and effectiveness of P/R-HRVBt for reducing stress and subclinical anxiety and depression, and to consider its clinical implications. Three databases (PubMed, PsycINFO, Web of Science) and reference lists were searched. Eligible studies were written in English, used P/R-HRVBt, and quantitatively assessed feasibility or effectiveness on psychological outcomes or physiological stress markers in adults experiencing stress or subclinical anxiety and depression. Thirteen studies met the inclusion criteria. Quality was appraised using the Quality Assessment Tool for Quantitative Studies. All studies received a global ‘weak’ rating, though four achieved ‘moderate’ quality when blinding was excluded. Overall, P/R-HRVBt was found to be feasible. All studies reported improvements in at least one psychological or physiological outcome, though heterogeneity in study design, measures, and effect sizes limited conclusions. Further high-quality research is warranted. Nonetheless, findings suggest that P/R-HRVBt may be comparable to established interventions and offers a promising alternative for improving psychological and physiological health.</p>