Apple's Smart watch has Electrocardiogram (ECG) feature which help to recognise heart beat. An Indian whose son gifted him Apple watch series 5. Old man named Rajhan, suffered from a low ejection fraction and required immediate heart surgery to replace his Mitral Valve. Due to COVID-19 surgery was delayed his Son Sidhartha told watch helped to detect irregular heart beat prior to Valve failure.
After Sucessfull surgery he thanked Tim Cook CEO of Apple
The most advanced technology wrist watch has very smart features, there is a very sensor which read heart beat if it more than 120 bpm or less than 40 bpm sent a notification to your Android or Iphone.
You can download your ECG rate also take it's print out. Which help you to find accurate data of Heartbeat.
This features available on Series 4 or later watches of Apple.