Is it possible to make Apple Watch Series 5 measure heart rate (pulse), passively, all the time? I bought an Apple Watch Series 5, because I wanted to measure my heart rate, passively, all the time (24/7).

However, I cannot find a way to enable the heart rate monitor, so that it's "on" by default.

Only by opening specific apps, like Pulse, I'm able to start the heart rate monitor, but as soon as I close that app, the monitor stops.

I know that Garmin Forerunner Fenix 5 monitors the heart rate all the time, without the any user-intervention, which is what I want to achieve on my Apple Watch Series 5. Is this possible?
Apple Watch 4 does this for me and has since day one. 

Tap show all data at the bottom of health App on your phone to see your samples of data. 



I don’t think you can change the default sampling rate, but I’m seeing samples every few minutes all day and all night. At 12 to 13 samples an hour it’s hard to see what you’re going to get by doubling the data. 

During a workout session the sample rate is even higher so you can get some very large datasets if you have long workouts.