North Otago started well in the game, which doubled as the Hanan Shield trophy, but was unable to sustain its effort for 80 minutes.
Its overall fitness appeared to be lacking, with a number of individuals waning for periods during the game.North Otago co-coach Barry Stevens accepted the effort was "a little disappointing".
"We put pressure on them and got in front, but we just let them come back," he said.
"It was just lapses of concentration. They scored three tries in a matter of 10 minutes, which brought them back into the game.
"These are the sorts of areas we’ll have to work on."
North Otago started brightly with centre Shae Tucker crossing for a try after three minutes.
Hooker Joe Pickett scored six minutes later.
Josh Casey converted both six-point tries to give North Otago a decent buffer.
Mid Canterbury responded through first five-eighth Jared Percival.
He looked the best of the opposition backs and carved through to score and convert.
Percival caught North Otago from the kickoff when he broke from inside his 22 and raced 70m to score.
And shortly before halftime loosehead prop Adam Williamson put Mid Canterbury into a 20-16 lead with an unconverted try.
North Otago regained the lead early in the second half when No8 Lucas Goodin drove through the defence and Casey raced 35m to score.
But Percival struck again, splitting North Otago’s tiring defence to score and put Mid Canterbury back in front.
North Otago replied when winger Simon Lilicama scored on debut.
However, Mid Canterbury finished the stronger of the two with late tries to halfback Will McKenzie and replacement three-quarter Timoci Nakekeke.
In other Heartland games, South Canterbury held on to beat Buller 28-26 after a late penalty attempt by Buller hit the upright.
Wanganui scored 10 tries as it beat West Coast 74-6, while Poverty Bay beat its northern neighbours, East Coast, 54-30.
King Country beat Wairarapa-Bush 18-16 and Horowhenua-Kapiti defeated Thames Valley 34-30.
- Terry O'Neill
Heartland championship
The scores
Mid Canterbury 40
Jared Percival 3, Adam Williamson, Will McKenzie, Timoci Nabekeke tries; Percival 2 con
North Otago 32
Shae Tucker, Joe Pickett, Lilicama Lilicama, Josh Casey tries; Casey 4 con
Halftime: Mid Canterbury 20-16