On some machines, the following sample doesn't work correctly.(heat map layer doesn't show up on the map)
Had the same issue with the heat map you can set on the ArcGIS Online's Web map.
After some investigation, there seems to have an issue with IE11 and Intel HD Graphics.
There are some threads on the web.
Well, this Google's sample app also doesn't work.
1. try Internet Options > Advanced > Accelerated grphics > Use software rendering instead of GPU rendering to be enabled
2. update the Intel HD Graphics' driver update
both worked in my case.
*IE10 didn't have this problem.