Today I connect my trainer via BT to my iPad. Everything works just fine.
But now I would like to connect my Garmin Fenix 3 that have my HR-belt connected, to my ipad to get heartrate in Zwift.
Is it possible?
You would need a Lightning to 30pin adapter and a Wahoo ANT+ key in your iPad to get the ANT+ signal to Zwift (I am assuming you are using a Garmin HRM that only broadcast in ANT+). You cannot use the Garmin Fenix to bridge the connection.
A better option is to get a Wahoo Tickr (or other HRM that is duel band) that broadcast in both ANT+ and Bluetooth so you will have a much more versatile setup.
Agree with Paul – a Tickr (or TickrX) is a better option. The Wahoo Fitness App is pretty useful, too.