I just tested to see of BC saves the Cadence data in a GPX and TCX file. No it does not, so I assume it does not save HeartRate data either.
I hope this isn't confusing, but here is a TrkPt from before/after of GPX & TCX saved data. The original .gpx was from an Oregon 450. I used TCX Converter to convert the .gpx file to a TCX file.
TCX file Before opening in BC:
<Trackpoint>
<Time>2011-06-04T17:26:02Z</Time>
<Position>
<LatitudeDegrees>47.544988</LatitudeDegrees>
<LongitudeDegrees>-116.334362</LongitudeDegrees>
</Position>
<AltitudeMeters>646.14</AltitudeMeters>
<DistanceMeters>0</DistanceMeters>
<Cadence>0</Cadence>
<SensorState>Absent</SensorState>
</Trackpoint>
TCX file After opening in BC & verifying Cadence is displayed in Properties/Elevation Profile then Saved as TCX file (no additional adding or moving TrkPts etc) :
<Trackpoint><Time>2011-06-04T17:26:02Z</Time><Position><LatitudeDegrees>47.544988039880991</LatitudeDegrees><LongitudeDegrees>-116.33436203934252</LongitudeDegrees></Position><AltitudeMeter
s>646.13999999999999</AltitudeMeters></Trackpoint>
GPX file Before:
<trkpt
lat="47.544982"lon="-116.334145"><ele>649.03</ele><time>2011-06-04T17:26:27Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:cad>45</gpxtpx:cad></gpxtpx:TrackPointExtension></extensions>
</trkpt>
GPX file After:
<trkpt lat="47.544988039880991" lon="-116.33436203934252">
<ele>646.13999999999999</ele>
<time>2011-06-04T17:26:02Z</time>
</trkpt>
Ron