LF/HF Ratio (Autonomic Tone) Calculator

LF/HF Ratio (Autonomic Tone): Explanation and Clinical Context The LF/HF ratio is a key heart rate variability (HRV) parameter reflecting autonomic nervous system balance. LF (low frequency) power represents both sympathetic and parasympathetic activity, while HF (high frequency) power is primarily a marker of parasympathetic (vagal) activity. The LF/HF ratio quantifies the relative contribution of sympathetic vs parasympathetic tone.

A higher ratio indicates sympathetic dominance, associated with stress, higher cardiovascular risk, and potential arrhythmic vulnerability. A lower ratio reflects parasympathetic predominance, linked with relaxation and cardiovascular protective effects. Balanced autonomic tone (LF/HF between 1–2) is considered physiologic in healthy adults.

This tool allows clinicians and researchers to estimate autonomic balance from HRV spectral analysis and helps in risk stratification for cardiovascular events, stress assessment, and monitoring of interventions such as exercise or pharmacotherapy.