As part of the Anglia Ruskin marathon pacing study we have to submit our heart rate data from the 2016 London Marathon. I wrote this little Windows program to get my data from the Garmin Connect website into CSV format for the ARU team. It's open source so you're welcome to reuse the code for your own purposes.
Download GarminGpxHrmToCsv.exe here. (Right click, save as... or just Run. But you'll have to accept some security warnings to do so.)
The program also shows this list of steps:
If it doesn't work for you, please email me your GPX file so I can investigate.
I'm releasing this under the Apache License v2.0 just to cover liability etc. This is a permissive licence allowing you to reuse the code in your own commercial programs if you wish.
Download GarminGpxHrmToCsv_v1_0_0_0_r3888.zip source code package.
It's a simple Visual Studio 2008 Windows Forms C# project. I created it in an old version of Visual Studio so that you should be able to open it with whatever version you have so long as it's not pre-2008.