Measurement and interpretation
HRV
Definition
Heart rate variability is the variation in time intervals between consecutive heartbeats, usually measured from normal-to-normal cardiac intervals.
Aliases and abbreviations
HRV · R–R interval variability · beat-to-beat variability
Editorial record
Published: August 25, 2026 · Reviewed: August 25, 2026
Expanded definition
HRV describes timing variation rather than the average number of beats per minute. Different time-domain and frequency-domain metrics emphasise different features of the signal.
Some short-term HRV measures are strongly influenced by breathing-related cardiac vagal modulation, but HRV also changes with posture, activity, sleep, stress, age, health, medication, recording length, and data quality.
A useful interpretation compares like with like: the same metric, measurement conditions, recording length, and person over time. One isolated value should not be treated as a diagnosis or a complete measure of autonomic health.
What the term does not establish
Why the distinction matters
HRV is widely used in nervous-system and VNS discussions, so distinguishing the measurement from the claims built around it is essential.
Main guide
A research overview of HRV metrics, standards, autonomic context, and interpretation limits.
Explore HRV researchRelated terms
Measurement and interpretation
Nervous system
Measurement and interpretation
Safety and research
Safety and research
Measurement and interpretation
Editorial scope
This glossary entry supports general education. It does not diagnose, recommend treatment, or transfer findings from one VNS method, protocol, or device to another.