HRV as a Biomarker: What Your Heart Rate Variability Actually Tells You
May 28, 2026 · 8 min read
Heart rate variability (HRV) is the single most informative non-invasive measure of autonomic nervous system function. Yet most people who track it do not understand what it actually measures.
What HRV Actually Measures
HRV does not measure your heart rate. It measures the variation in time between consecutive heartbeats. High variability indicates that your autonomic nervous system is adaptable.
The Key Metrics
RMSSD
The gold standard for parasympathetic activity. RMSSD reflects beat-to-beat variations and is highly sensitive to vagal tone.
SDNN
A broader measure of overall HRV that captures both sympathetic and parasympathetic influences.
LF/HF Ratio
The ratio of low-frequency to high-frequency power. A declining LF/HF ratio indicates a shift toward parasympathetic dominance.
Why It Matters
HRV is not a wellness metric. It is a clinical biomarker with established correlations to all-cause mortality, cardiovascular risk, cognitive function, and immune response.