Heart Minutes are defined as minutes spent by a person with an elevated heart rate during exercise. Uniquely, each of the Health Kits we plug into calculate it the same way. This elevated heart rate data is calculated based on recommendations from the World Health Organization: https://www.who.int/news-room/fact-sheets/detail/physical-activity
If the heart rate monitor says you're working at 50-60% of your max heart rate, then the exercise is considered moderate. If the heart rate monitor shows that you're working at 70-85% of your heart rate then it's vigorous exercise.
To find your maximum heart rate, subtract your age from 220.
Here is an example for someone age 45.
220 - 45 = 175
175 ÷ 2 = 87.5
If your heart rate is above 87.5, you would be in the moderate range for a heart minute.