4iiii Viiiiva HRM as Bluetooth bridge

I am having low cadence readings too. I switched from a desktop Mac to Apple TV4K and picked up a 4iiii heart rate monitor to bridge my Garmin speed/cadence sensor to Bluetooth. My trainer is a Kickr Snap. Zwift looks much better on the ATV but I am not getting reasonable cadence readings. I can be pedaling easily at 90+ rpm but the reading on Zwift will be only about 65. Sometimes I can stop pedaling and the reading will remain at 65. Occasionally I can drop cadence to 40 and the reading will climb up into the 70s. If I shut Zwift down and start the 4iiii app on my phone, the cadence reading will be correct.

I cannot figure out where in the process, sending or receving, the problem exists so I don’t know who to contact.

There is a known step you have to take with the Viiiiiva HRM to pair it to Zwift. Because you’re able to pair and pass data to the game app, I’m not sure that this is going to help your specific case, but it’s worth double-checking.

Have you tried updating the firmware on the 4iiii HRM? It’s possible that even out of the box, it needs an update.

Thanks for the advice but it looks like the device is up to date. It is running 2.0.0 firmware.

Did you check the known step in the first link I provided, and the part about the HRM’s default name?

Yes. I renamed the HRM to Viiiiva and now it does not seem to work as anything but a heart rate monitor. It is no longer picking up data from the Garmin speed/cadence sensor.

This morning the ANT link was not working at all so I removed the Viiiiva’s batter for about an hour. Before reinstalling the battery I removed the HRM from the devices lists on Zwift and the Viiiiva phone app. Installed the battery and started fresh. With Zwift off I paired the HRM with the Viiiiva app, checked that it worked, then added the Garmin ANT+ speed/cadence sensor. While I did not receive a message that the Garmin sensor had been detected, turning the crank showed that the signal was being received. Low rpm and high rpm read correctly. Next step was to start Zwift. I had to choose the HRM from the list and the same for speed/cadence. Both seemed to register appropriate readings on the devices screen so I started a ride. I had time for only five minutes, but all readings seemed appropriate. Changes in cadence seem to require three to four seconds to register, but I was able to see 40 rpm to 110 rpm and back to zero. I ran through this a few times and the readings remained consistent. I admit that I did have a bit of worry the first time I ran the rpm up through the 60-ish range.

I’ll see if this sticks tonight or tomorrow.


So far, so good.


I’m back to the Viiiiva not working again. Low cadence readings have been occurring pretty regularly (confirmed by operating my Garmin Edge Explore simultaneousy) and now I’ve lost heart rate readings. Garmin was picking up HR but it was not appearing on Zwift. I reset all of the components again and now I can receive HR only with the phone App. Additionally, the phone app will no longer pair my Garmin speed/cadence sensor. Error message every time.

Have you tried replacing the batteries on the Garmin sensors?

Even replaced the new battery in the Viiiiva. All of the components work flawlessly on their own, but when they need to interact it all goes wrong. I purchased the Viiiiva strap in order to avoid replacing ANT+ components already on multiple bikes. It may be better to just get a set of the readily transferable Garmin strap-on sensors and ditch ANT+ altogether.