When a pawn has a vanilla heart attack they go through the stages of painful ect. presumably the heart has already stopped at this point and the medic who is "tending" is attempting CRP
this is vanilla rimworlds version of death rattle i guess.

Would it be possible to make the heart attack destroy the heart (if the vanilla CPR attempts fail) rather than killing the pawn?

This would be especially useful as in the case of heart attacks you may have already rescued the pawn back to the base, where you are likely to have a spare heart / harvest a prisoner