Chris Lynn marked his home debut with a blistering innings of 83 from just 43 balls, with Australian opener smashing eight sixes and four fours as he shared a fantastic opening stand of 149 with Ben Curran, who hit 71 from 43 balls.
The pair set up the Steelbacks for a huge total of 223 for four, but for much of the innings it looked as though the visitors may well overhaul that mark until Heldreich stepped up.
The 20-year-old changed the game, claiming three for 22 from his four overs as Durham completely lost their way and slumped from 150 for three after 13 overs to 192 all out.
The win was a great response from the Steelbacks to their 125-run defeat at the hands of Birmingham Bears on Thursday, and sets them up nicely for Monday's trip to Trent Bridge to take on Notts Outlaws.
Steelbacks made one change to the team thumped at Edgbaston on Thursday, with James Sales left out and Graeme White taking his place.
After skipper Josh Cobb won the toss, the Steelbacks set about putting their opening day nightmare behind them and giving Durham a big target to chase.
By the end of the six-over powerplay they were 59 without loss, with Lynn having smashed two huge sixes, one out of the ground and in the direction of the Wellingborough
Road and the other on to the roof of the old indoor school.
Ben Curran played his part too with a batch of fours, and the Steelbacks were well set.
By the halfway mark they were 93 for nought, and it was Lynn who won the race to 50, coming off 32 balls.
Curran wasn't far behind him though, bringing up his half-century in 35 balls, including nine fours.
Steelbacks were taking full advantage of some ragged bowling from Durham, with Ben Raine in particular having a shocker - bowling three no balls for height in the same over and being ordered out of the attack by the umpires.
Lynn and Curran were having a field day, but their fun came to an end in the 14th over when Curran chanced his arm once too often and was caught at extra cover for a superb 71 from 43 balls, hitting 12 fours and one six.
Saif Zaib then went next ball as Ashton Turner picked up two in two, but it was only brief respite for Durham.
Lynn hit three sixes in the 15th over before Cobb perished going for a big hit, and sadly for the home fans the Australian went himself off the final ball of the 17th over, caught in the deep.
He made 83 from 46 balls, hitting four fours and eight sixes - including three out of the ground.
His departure didn't mean the end of the big-hitting though as Rob Keogh clubbed a couple of his own in a quickfire 36 not out from 21 balls to lift the Steelbacks to an imposing 223 for four in their 20 overs.
Durham started their innings in blistering style as they set about their chase as they raced to 60 without loss in four overs, but Matt Kelly made the welcome breakthrough as Michael Jones mistimed a pull to Saif Zaib at deep mid-wicket.
It didn't stop the flow of runs though as Durham ended the powerplay ahead of the run-rate on 85 for one, bringing the required rate down to below 10.
They did lose skipper Ashton Turner to a shoulder injury as he dived in for a quick single, but they had powered along to 114 for one when Heldreich struck a crucial blow, having Graham Clark caught behind for 54.
In the next over Graeme White bowled Paul Coughlan for a duck, and there was suddenly hope for Steelbacks with Durham 117 for three.
They had moved to 150 for three in the 14th over, which was Heldreich's last, but it proved a fruitful one for Steelbacks as the left-arm wrist spinner claimed two wickets in two balls, snaring the dangerous David Bedlingham for 30 and Ned Eckersley for a first ball duck.
Durham's self implosion continued in the next over as Brydon Carse offered up a simple catch to Heldreich off Sanderson, and they were now in bother at 158 for six - the required run-rate creeping above 12.
The Steelbacks were scenting blood, and in the next over they snared two more wickets, with Cobb doing the damage this time as Durham's batters tried to hit their way out of trouble, only to hole out on the boundary and they were 163 for eight.
Durham hit 16 off the 17th over, bowled by Kelly to rekindle their hopes and they needed 44 to win from the final 18 balls.
But that proved beyond them, and with Turner not fit to bat, when Ben Sanderson dismissed Scott Borthwick in the 19th over that was that.