No signs of it yet on my Galaxy 6 classic/S24U in the UK. Only available in certain countries. I think if it is available it shows up in settings->notifications in the ecg section of the Samsung Health Monitor app on the phone. I believe it also gives a pop up asking if you want irregular heartrate notifications on recording your first ecg. I believe when available the watch only checks for irregular rhythm a 'few' times a day and requires the heart to be irregular for an hour before sending a notification. But you can get notifications now on fast or slow heart rates which are more immediate, not the same thing as irregular I know but may be helpful. That's set in the Wearable app, navigate to Watch settings->Samsung Health->Heart rate. You can set your thresholds for detection.
