In previous versions the Garmin GPX file import plugin included support for reading heartrate information, but only from Garmin Training Center TCX files. The Garmin plugin will now read heartrate from Nike device files exported as GPX files. There is to-date unfortunately no standard for presenting this information; this release of the plugin looks for <gpxtpx:hr> tags in the GPX file. This change may support additional device exports. Unfortunately the lack of standardization makes it impossible to say.
The updated plugin is not currently included with any release (it will be with the next update) but is available as a separate download. If you're interested, download www.dplot.com/plugins/fileimport/garmin.dll. Save this file to the \plugins\fileimport folder below the folder where dplot.exe is installed. (The default location is c:\Program Files\DPlot or c:\Program Files (x86)\DPlot on 64-bit systems.)
Of course if you have a GPX file containing heartrate information that is not supported by DPlot, please let us know.
As an aside this came to me from an old (emphasis on old) friend whose file showed a maximum heartrate of 208! I threatened to rat him out to his wife, before he informed me that it was recorded by his 13-yr old daughter. Well, OK then.