I don’t know what the full story is. However, the issue with pre-existing conditions is different from the issue with approved treatments.
The pre-existing condition problem would apply if you had, say cancer, and then got insured, and wanted treatment for the disease you had before you got insured.
The approved treatment issue is IPAB or “death panel” related. They could say that if you’ve ever had condition (a) (in this case heart problems), that treatment (b) (in this case chemo) isn’t cost effective because it’s unlikely to prolong your life.
That might be what is going on here. The ACA may be more generous about pre-existing conditions, but stingier on what types of treatments it covers.
I can only go by what is presented here (and it doesn’t seem to be full or complete) ...
“... but because of a previous heart condition, it did not cover the treatments he needed for his cancer.”
That sounds like excluding because pre-existing conditions.