# Heart rate variability (HRV)

Heart rate variability (HRV) is the tiny beat-to-beat change in the time between your heartbeats, measured in milliseconds. Within a healthy sinus rhythm, higher values usually reflect stronger vagal (rest-and-digest) control and a more adaptable heart. But not all variability is good. Pathologically high beat-to-beat swings, as in atrial fibrillation or frequent extra beats, do not mean good autonomic health, and you must rule them out first. A falling HRV trend is linked to aging, chronic stress, and higher all-cause death risk.

## Sources

- Malik M, Bigger JT, Camm AJ, et al.. (1996). Heart rate variability: Standards of measurement, physiological interpretation, and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. European Heart Journal. https://doi.org/10.1093/oxfordjournals.eurheartj.a014868
- Shaffer F, Ginsberg JP. (2017). An Overview of Heart Rate Variability Metrics and Norms. Frontiers in Public Health. https://doi.org/10.3389/fpubh.2017.00258

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