I've done this before by exporting the KML of the data and importing it into a Fusion Table[1] which has a built-in heatmap view. I tried to do it just now and not only have they nerfed it by only allowing you to download a 30 day range, the KML file they export doesn't seem to be readable by Fusion Tables. Disappointing.
Looks like you can still download all of your data from Google Takeout[2], though. The format is pretty easy to read, converting it into something that Fusion Tables can read should be pretty easy.
The export limit is limited to 30 days only by the UI, if you do a request but change the timestamps you can get any range of dates. This will get you all your data as a KML from 1/1/2005 to 1/1/2015:
Looks like you can still download all of your data from Google Takeout[2], though. The format is pretty easy to read, converting it into something that Fusion Tables can read should be pretty easy.
[1] http://www.google.com/drive/apps.html#fusiontables
[2] https://www.google.com/settings/takeout/custom
EDIT: I modified a json->CSV jsfiddle I found so it converts the data I got from Google Takeout to something that is readable by Fusion Tables:
http://jsfiddle.net/evan/5w9Hz/embedded/result/
However, Fusion Tables thwarted me again by only showing a heatmap of the first 1000 location records, so I'm giving up on this for now.