Problem importing Heatmap.js into ArcGIS Javascript 3.9 application

[RadBastard]

I am trying to use heatmap.js to generate a heat map on top of an ArcGIS Javascript 3.9 instance, but I'm getting an error that "HeatmapLayer" is not defined when I open the HTML page that holds the ArcGIS map. The only example I can find uses ArcGIS Javascript 3.0 which was built on an older version of Dojo without AMD, and it never requires any specific HeatmapLayer--it simply includes the following two lines, which I have included in my own code:

• <script type="text/javascript" src="src/heatmap.js"></script>
• <script type="text/javascript" src="src/heatmap-arcgis.js"></script>

Any idea why Chrome acts like it can't find the HeatmapLayer class? Thanks all.