Is the Vivoactive 3 compatible with all Garmin chest HR straps?
As long as they're ANT+, they'll be compatible.
If you have a chest HR from something like a FR301 which is probably 20 years old, it will only transmit ANT (without the +).
I have a Magene H64 and it works like a charm. As long as they support ANT+ you are fine. If you like cheap and reliable you might consider that one from Aliexpress, sells at ridiculous prices.
