As pointed out in #1208 heatMap has no support for any axis customization aside from keyAccessor, valueAccessor, rowsLabel, and colsLabel. If it inherited from coordinateGridChart, you'd be able to add axis labels, customize the number of ticks on the axes, format the tick labels easily using scale domain, and more.
Personally, I am probably just going to add a bunch of the functionality from coordinateGridMixin.js to my chart's pretransition, but heatMap is based on a coordinate grid enough so that it would make sense to integrate the two.
Is there a reason heatMap doesn't do this, or has it just not been gotten around to yet? (apologies if there's a good reason for this, please help me understand!)