What is Heart Rate Variability and Does It Matter?
New access to an old idea
Heart rate variability is one of a plethora of measurements reported by many wearables such as heart rate monitors, fitness and wellbeing monitors. The concept of HRV is nothing new, however - it has been around in the medical literature since 1733! What is definitely new is that ability to measure this useful metric in real-time, and integrate it into understanding your own health.
This guide explains what heart rate variability is, what is normal, what sudden changes may mean, and when changes in HRV may warrant further investigation.
What is heart rate variability (HRV)?
Heart rate variability refers to the small, natural changes in time between each heartbeat. Although your pulse may feel steady, the interval between beats is constantly adjusting from moment to moment.
These variations are controlled by your autonomic nervous system — the balance between your “fight or flight” response and your “rest and digest” response. A healthy heart does not beat like a metronome. Instead, it responds dynamically to breathing, activity, stress, sleep, and recovery.
HRV is usually measured using:
24-hour ECG (Holter monitor)
Longer-term event monitors
Implantable loop recorders
Some wearable devices
Is high or low HRV better?
In general:
Higher HRV is usually (not always) associated with good cardiovascular fitness and resilience.
Lower HRV can be linked to stress, fatigue, illness, or underlying heart conditions.
However, HRV is complex. A low reading on a fitness tracker does not automatically mean a diagnosis of heart disease. Equally, a high HRV does not rule out arrhythmia (onset of atrial fibrillation, for example, can cause a sudden increase in HRV).
For patients concerned about abnormal heart rhythms such as atrial fibrillation or supraventricular tachycardia, HRV alone is not a diagnostic tool. A full cardiac rhythm assessment is far more important.
What can sudden changes in HRV mean?
A sudden drop or unexpected change in your HRV can understandably cause concern — particularly if you monitor it regularly using a wearable device.
It is important to emphasise that HRV is a non-specific measurement. Sudden changes do not automatically indicate a serious heart problem but may be a useful starting point for further evaluation.
Possible causes for a sudden change in HRV include:
Heart rhythm changes (arrhythmia) including atrial fibrillation, ventricular tachycardia, heart block and ventricular ectopics
Non-cardiac causes
Viral infections (including common respiratory viruses)
Fever or inflammation
Dehydration
Poor sleep
Psychological stress
Overtraining or physical exhaustion
Alcohol consumption
In fact, many patients notice a drop in HRV in the days before developing viral symptoms. This reflects changes in the autonomic nervous system rather than a primary electrical heart problem.
Because HRV is influenced by so many factors, an isolated abnormal reading — particularly without symptoms — is rarely diagnostic. Persistent symptoms such as palpitations, blackouts, chest discomfort, or breathlessness are far more important indicators for further investigation.
Can HRV detect heart rhythm disorders?
HRV can sometimes provide clues, but it does not diagnose arrhythmias on its own.
Conditions such as:
Ventricular tachycardia
Bradycardia (slow heart beat)
require proper ECG monitoring and expert interpretation by a cardiologist or cardiac electrophysiologist.
The bottom line
Heart rate variability is a normal and healthy feature of the human heart. While sudden changes in HRV can occasionally reflect arrhythmia, they are often caused by non-cardiac factors such as viral infection, stress, or fatigue.
If you are concerned about palpitations, irregular heartbeat, or unexplained symptoms, a specialist heart rhythm assessment provides far more meaningful information than HRV data alone. Early expert evaluation can offer reassurance — or identify treatable conditions before they become more serious.