Apple Watch Series 12 records lower heart rate and more frequent low HR alerts

Old_Dog_Hawaii wrote:

Apple watch series 12 records my HR (swimming workouts, stairs, sleeping, etc.) about 10 BPM lower than all of my previous apple watches have. Years of experience yielded the similar HRs for all my activities. I also have had A-Fib so I pay more attention to HR than most folks. Also, I used to get a reading (while asleep) about once or twice a month that my HR had fallen to below 39 BPM for an about 15-30 minutes. Now with the "12", it happens every night. Always 15 to 90 minutes before waking for the morning. I have worn an apple watch for many years and think can see this very noticeable difference in HR measurement. I am using the same watch bands (NIKE Sport) for all of them Any one else notice this?

Using an iPhone 17 and MAC OS 27

I suggest that you download InstantHeartRate, it's an app for your iPhone. I believe there is a free version. Compare its heart rate measurement while you are sitting quietly with the heart rate measurement from your Apple Watch. I don't have the Series 11, I have the Series 10, but mine measures a heart rate very close to that app. Another way to check: since you have AFib I imagine you go to a clinic now and then ... next time compare your watch pulse measurement with the one they do in the clinic. These are not solutions but may help you understand better if the Series 11 measurement is correct.

Your mention that you have been using the same watch band for all your watches is pretty compelling as it seems to rule out the fit of the band causing this. That said, different models of watches can be different sizes and mass and may sit on the wrist/arm differently.

It is not uncommon for the pulse to reach a minimum shortly before or when awakening from sleep. Mine does that too, and I have 40 set for my low rate notification and I get one every morning. If I am sitting very quietly, say reading, I sometimes get notified that I am below 40 for ten minutes. My resting pulse is usually in the low 40s, this is noticed at every physical, but since I am a long distance cyclist, they attribute it to the exercise. However what is measured in the clinic and with that iPhone app and with my watch all agree quite closely. It would be good to know if your watch agrees with other independent measurements or is an outlier.

I would also encourage you to revisit the band and fit of the watch. I always tighten mine by one notch before a workout because it doesn't maintain good contact when my arm is in motion for the pulse measurement unless I do that. The part of the Series 12 watch that contacts the arm and has the sensors looks different from the Series 11, so it might be that the fit has to be rechecked with a different model of watch.f

Thanks Steve, Yes, my use of the watch pretty much is like yours. I have had every Apple watch since 2016 (I buy a new one every year) and the HR they recorded all were the same except the new "12". The reading from the "12" is the same as my other HR monitors but only when sitting, including my 5 lead KARDIA.

But when doing anything (walking, climbing stairs, swimming, etc.) that is when there is a variance from the last 10 years to what I am seeing now with the "12". For instance, a 40 minute swim workout has always yielded an avg 134-137 HR for the last 10 years but now with the '12" it is always around 122 to 126 now. That is a lot of difference. Also, I used to always get up to the low 140s now the best I can do is maybe getting to 131 or so. Strange.