Heart rate variability (HRV) measures the variation in the time interval between successive heartbeats, reflecting the influence of the autonomic nervous system (ANS) on heart rate (HR) changes. This review provides an extensive overview of HRV measurement techniques, their applications, and their limitations in healthcare, exploring their potential for prognosis and condition assessment. A scoping review was conducted, gathering literature reviews on HRV spanning the past fifty years using PubMed, Scopus, and Web of Science databases. Our findings identified significant research gaps, including contradictions in the literature and the absence of standardized protocols for HRV measurements, which complicate the establishment of consistent baseline values. Additionally, the lack of protocols for pulse rate variability (PRV) in the context of advanced sensor technology hinders progress in HRV research. Despite these challenges, HRV remains significant in assessing cardiac autonomic function and its potential clinical applications. However, barriers such as device unfamiliarity, data accuracy concerns, and a lack of clinical trials limit its adoption. Further research is required to elucidate the relationship between abnormal HRV and health problems and to establish consistent baseline values for advancing HRV applications.