The emWave and Inner Balance systems calculate coherence by analyzing the symmetry of your wave-like HRV patterns. Every few seconds, the proprietary algorithm determines the “orderliness” of the rhythm.

In the Power Spectrum view, you can see this balance visually:

The Left Region (Sympathetic): Blue bars here indicate “fight or flight” activity. In low coherence, bars are often scattered or concentrated here.
The Right Region (Parasympathetic): Bars here represent the “rest and digest” activity.
The Center Region (Coherence): This is the synchronization zone. In High Coherence, the blue bars focus in this central area and increase in amplitude, showing that both branches of your nervous system are perfectly synchronized.

It is important to note that Coherence scores are distinct from traditional HRV measures like SDNN. While SDNN measures the total volume of variability (how much it changes), Coherence measures the mathematical order of that variability (how smoothly it changes).

The Relationship Between HRV and Coherence Scores

Understanding the data behind your HeartMath sessions is key to mastering your physiological state. This guide explains how Heart Rate Variability (HRV) is translated into the coherence scores you see on your screen.

What is a Coherence Score?

A coherence score is a measurement of the symmetry and rhythm of your heart rate patterns. Unlike heart rate (which is just beats per minute), HRV looks at the small changes in time between each beat. When these changes occur in a smooth, rhythmic wave, you are in a state of high coherence.

The Three Levels of Coherence

Low Coherence: Indicates little to no wave-like activity. The rhythm is typically jagged, reflecting a nervous system that is out of sync.
Medium Coherence: Indicates the emergence of a wave-like pattern.
High Coherence: Indicates a highly symmetrical, sine-wave-like pattern. This is the “zone” where your body is performing at its most efficient level.

Reading the Power Spectrum

The Power Spectrum graph provides a real-time look at your Autonomic Nervous System (ANS). It is divided into three distinct color-coded regions:

Sympathetic Activity (Left Side): Often associated with energy expenditure and stress responses.
Parasympathetic Activity (Right Side): Associated with recovery, relaxation, and digestion.
Synchronization (Center): This is the Coherence zone. When you reach High Coherence, the blue bars migrate to this center region and grow in height (amplitude), signaling that your sympathetic and parasympathetic branches are working together in harmony.

Coherence vs. Traditional HRV Metrics

It is common for users to compare coherence scores to traditional medical HRV parameters like SDNN. However, they measure different things:

Traditional HRV (e.g., SDNN): Measures the amplitude or the total amount of variability.
Coherence: Measures the pattern and order of the variability.

Because coherence focuses on the rhythm rather than just the amount of change, you can have a high coherence score even if your total variability amplitude is relatively low.

Technical Note

The mathematical algorithm used to derive coherence ratios is proprietary to HeartMath. The software stores data points every half second to ensure a smooth and accurate representation of your heart’s rhythm. For the best results, focus on Heart-Focused Breathing to naturally shift your Power Spectrum toward the central synchronization zone.