Apple Health metrics › Heart Rate Variability (HRV)

Heart Rate Variability (HRV) on Apple Watch and iPhone

The beat-to-beat variation in your heart rhythm, often used as a recovery and stress signal.

What it is

HRV measures the tiny differences in time between heartbeats. Higher variability generally reflects a body that adapts well to stress, while a sustained drop can mean strain or poor recovery.

How Apple measures it

Apple Watch records HRV as SDNN in milliseconds, in short samples taken mainly while you are still and during sleep. Apple's SDNN is not directly comparable with RMSSD numbers from other devices.

What's a normal range?

HRV differs widely between people and falls with age. Typical adult SDNN values span roughly 20 to 100 ms or more, so compare against your own rolling baseline, not other people.

What moves it

• Sleep quality and duration
• Alcohol (strongly lowers it)
• Hard training or overreaching
• Illness onset
• Stress and travel

See Heart Rate Variability (HRV) next to your other vitals

Apple Health keeps this number several taps deep. OnlyVitals puts the metrics you pick, including Heart Rate Variability (HRV), on a single dashboard so you can read them at a glance. Everything stays on your device.

Frequently asked questions

Is a higher HRV always better?

Within your own baseline, higher usually reflects better recovery. Comparing your number with someone else's is not meaningful, because baselines differ a lot.

Which HRV metric does Apple Health use?

Apple Health stores SDNN in milliseconds. Many other apps report RMSSD, so the numbers do not match across platforms.

Related metrics

• VO2 Max (Cardio Fitness)
• Blood Oxygen (SpO2)
• Respiratory Rate
• Steps
• Sleep Duration
• REM Sleep

This page is general information, not medical advice. Ranges vary by age, sex, fitness and device. Talk to a clinician about anything that worries you.