If you notice your heart rate sampling intervals increase to 6 minutes, 30 minutes, and finally 2 hours in spite of your configured sampling interval while you are awake, it is a sign that the Cardiogram WearOS app is being restricted by an Android battery-optimization known as App Standby Buckets.
To maintain heart rate sampling at your configured interval on WearOS devices, please launch the Cardiogram WearOS app periodically, ideally at least once a day. Launching the app should be sufficient, and you can leave the app shortly afterward.
While we recognize that this is not ideal, it is an unfortunate necessity due to battery-optimizations known as App Standby Buckets, introduced in recent versions of WearOS (System version “H” or newer). In particular, under these battery optimizations, as our app becomes less and less actively used, the frequency with which we can schedule alarms becomes increasingly restricted and prevents us from measuring your heart rate in a timely manner.