What 'heartlands' would those be? They don't own them anymore.
Oddly enough, I think he will deliver for these areas. This is a particular obsession of Dominic Cummings and I would expect to see this happen in a big way.
Mind you, I'd guess there's also a calculation that, five years down the road from Brexit, a lot of the remain-voting ex-tory constituencies in the south will come back into the fold, too.
With boundaries being re-drawn to take away their current advantage and them being dead in Scotland, I wouldn't give you tuppence for Labour's future chances of forming a majority government.