Currently, the Stryd apps for iPhone and Android do not connect with a Bluetooth Heart Rate monitor.
Our developers are working on integrating Heart Rate into the app but the timeline is unknown. If you would like to be able to view your heart rate data and Stryd Power we do have a recommendation for iPhone users: "iSmoothRun"
iSmoothRun can use Stryd as well as a Bluetooth heart rate monitor. This data can also be exported to PowerCenter for better analysis and let you continue to build your Stryd profile.