Peter O'Malley shot a 2-under 68 on Friday to finish alone in second place at 8-under-par 132. Chris Downes carded a 3-under 67 and is in third at minus 7.
Heaven started poorly with a bogey at No. 1 but calmed down with four consecutive pars. He birdied the next two holes and completed the front nine at 1-under par.
'I had a bit of a nervous start, bogeyed the first hole, but that actually settled me down and after a few pars I finally got it back with a birdie on six,' said the 23-year-old.
He birdied his first two holes on the second nine and added a third at the par-4 17th to go two clear of the more experienced O'Malley.
Heaven is a senior business major at the University of Toledo and credited his time in the United States as helping him take the lead halfway through his national championship.
'I think my experience in the States has helped because they get good crowds for amateur tournaments so I feel I'm prepared for this,' said Heaven.'But being in this position is a new experience for me. I'll be playing next with guys who are right at the top of their game but I'm looking forward to it and I'll try as best as I can to enjoy the whole thing.'
Stuart Malcolmson (64), Terry Price (65) and Martin Doyle (64) share fourth place at 6-under-par 134. Euan Walters (69), Craig Jones (68), Kurt Barnes (69), David Diaz (69), David Smail (68) and Matthew Millar (70) are tied for seventh at minus 5.