Samsung Galaxy Watch records HRV automatically during sleep and while you are resting, and lists it in Vitals in Samsung Health once a week of nights has built your baseline Baseline Your own usual HRV level and range, built from weeks of readings taken the same way. Comparing a reading with your baseline says more than comparing it with other people. More about Baseline (Samsung Newsroom; Samsung Support). Samsung does not publish which HRV formula it uses, so its number cannot be matched exactly to RMSSD RMSSD Root mean square of successive differences: an HRV metric built from how much each heartbeat interval differs from the next, in milliseconds. It mainly reflects vagal activity. More about RMSSD or SDNN SDNN The standard deviation of all NN intervals in a recording, in milliseconds. It measures overall variability, and its value depends strongly on how long the recording lasts. More about SDNN norms.
Documentation checked: 20 October 2026. Samsung updates its watches and app often, so details can change.
What number Samsung shows
Samsung describes its HRV feature as analysing minute-to-minute variations in the intervals between heartbeats to show the balance of the autonomic nervous system Autonomic nervous system The part of the nervous system that runs the body without conscious control, including heart rate. HRV mostly reflects how it adjusts the heart from moment to moment. More about Autonomic nervous system (Samsung Newsroom). It does not name the statistic. The watch reads your pulse with the optical heart rate sensor PPG An optical method that shines light into the skin and detects the pulse of blood with each heartbeat. Most watches, rings and phone-camera apps use it to estimate HRV. More about PPG in its BioActive sensor, which also holds an ECG ECG A recording of the heart's electrical activity, taken with electrodes on the skin. ECG-based RR intervals are the reference standard for measuring HRV. More about ECG sensor and a body composition (bioelectrical impedance) sensor.
On the watch, HRV is one of five measures in Vitals: heart rate, breathing rate Breathing rate How many breaths you take a minute. It moves HRV on its own: slower, deeper breathing makes the beat-to-beat swing larger, and below about 9 breaths a minute it shifts from the HF band into LF. More about Breathing rate , skin temperature, blood oxygen and heart rate variability. Swipe to the Vitals tile and tap it to open the tracker; from the bottom of the tile, Show on phone opens the same data in Samsung Health on your phone (Samsung Support). Samsung’s support page describes Vitals on the Galaxy Watch9 and Watch Ultra2.
When Samsung measures
Samsung says HRV is recorded automatically during sleep and while you are resting (Samsung Newsroom). Vitals uses the measures taken while you sleep. If you have just got the watch, Samsung says you need to wear it to sleep for 7 nights to build your baseline before Vitals shows your data (Samsung Support).
How to read it
Vitals compares your nights with your own baseline and looks for significant changes (Samsung Support). That is the comparison to use:
- Compare with your own past values. Without a published formula, the number cannot be placed on RMSSD or SDNN tables.
- Look at the trend over a week or more, not a single night.
- Read the other four measures next to it. Vitals tracks them together, and a change in HRV is easier to understand when you see what else changed that night.
Samsung also builds HRV into its Energy Score. It combines sleep time and consistency, bed and wake times, sleep timing, the previous day’s activity, sleeping heart rate and heart rate variability. It needs data from a Galaxy Watch4 or later, synced with Samsung Health, and at least the previous day’s activity and sleep (Samsung). Samsung does not publish the weights. Recovery scores explained sets it next to other makers’ scores.
How Samsung compares with other devices
No current Galaxy Watch was part of the 2025 Dial study, which tested Oura, WHOOP, Garmin and Polar devices against a chest-strap ECG overnight (Dial and colleagues, 2025), and we found no other independent overnight study of a current Galaxy Watch.
An older Samsung watch, the Gear Sport, was tested in 2022. In that study, 28 adults wore it for 24 hours next to a chest ECG during their normal routines. During sleep, the time-domain HRV measures agreed acceptably with the ECG. While people were awake, most HRV measures had large errors (Sarhaddi and colleagues, 2022). The Gear Sport is not a current model, so the result shows a pattern rather than the accuracy of today’s watches: readings during sleep held up much better than readings while awake.
The HRV by device guide compares Samsung with the other brands.
What to watch out for
- Wear it every night for the first week. Without 7 nights there is no baseline.
- Daytime readings are a different measurement. Samsung also records HRV at rest during the day; keep your trend to sleep values.
- Keep the watch on the same wrist, at the same tightness. That keeps your nights comparable.
- Expect a step after a new watch or an update. See can a software update change my HRV.
- Do not mix brands in one trend. A value from another device is a different series. See is wrist HRV as accurate as a chest strap for how wrist and chest readings differ.