Sleep HRV

Sleep HRV shows your overnight heart rate variability, measured as RMSSD from the beat-to-beat recordings your Apple Watch makes while you sleep. Next to it is your average resting heart rate for the night. Apple Health's own HRV figure is SDNN, taken from short readings during the day. A 2026 review of the research recommends RMSSD as the default heart rate variability measure for sport and exercise. Each night is one point on the chart. The darker line is your 10-day average and the shaded band is your usual range over the last 60 days, so one rough night doesn't look like a trend. Tap a dial to switch the chart between HRV and resting heart rate. Tap the date to see that night's details: the HRV and heart rate ranges, your sleep and wake times, how many samples the Watch recorded and how many times you woke. The widget shows last night's values and a 10-day trend on your home screen. On Apple Watch, the Sleep HRV app shows the latest values and the complication puts last night's HRV on your watch face. With Background App Refresh on, the app updates itself shortly after you unlock your phone in the morning, so you don't need to open it. If you use intervals.icu, you can turn on sync and each night's HRV values (RMSSD and SDNN), resting heart rate and sleep time go to your own wellness page there, next to your training. Everything is worked out on your iPhone. Sleep HRV reads from Apple Health and never writes to it. You don't make an account and nothing is sent to us. Requirements: iPhone with iOS 18 or later, and an Apple Watch worn overnight with sleep tracking on. The Watch app needs watchOS 26. Your first values appear the morning after your first night. Sleep HRV is for your own interest and training. It isn't a medical device and it doesn't give medical advice.