Hichrismzai ,
Thanks for asking about the Heart Rate app on Apple Watch.
Make sure you are on the latest version of iOS and watchOS supported by your devices. In addition, take a look at the following articles to help with making sure your Apple Watch is calibrated correctly and for more information on monitoring your heart rate with the Heart Rate app on the Apple Watch.
Calibrating your Apple Watch for improved Workout and Activity accuracy
Monitor your heart rate with Apple Watch
If the issues remain, please ensure you are wearing the watch correctly as per this help article: Wearing your Apple Watch
Regards