Even after 4–5 months, these readings may say “Trend Unavailable” if your Apple Watch hasn’t collected enough suitable background heart-rate measurements. Wearing the watch regularly helps, but it doesn’t guarantee that every metric will be available.
Try these checks:
- On your watch, open Settings -> Privacy & Security ->Health -> Heart Rate and make sure heart-rate tracking is enabled.
- Wear your watch snugly during the day so it can collect reliable readings.
- On your iPhone, open Health -> Browse -> Heart -> Resting Heart Rate and Walking Heart Rate Average to see whether individual readings are being recorded.
If there are no readings, check More info: Monitor your heart rate with Apple Watch.