The Gloucester captain is set to make his Test debut at the relatively advanced age of 32 when England face Wales at Twickenham on Sunday in the first of their four warm-up matches for the upcoming Rugby World Cup in Japan.
A native of Christchurch in New Zealand's South Island, Heinz played for the local Crusaders franchise before joining Gloucester for the 2015/16 season.
Heinz, however, is England-qualified through his late grandmother, Aylieff, who he said had been a big influence on his life.
"My grandmother -- my mother's mother -- - was born and raised in a little place called Bishop’s Waltham near Southampton," Heinz told reporters at England's training base after being named on Friday in the team to play Wales.
"She met my grandfather, who was with the New Zealand Navy, in World War II. She was a Wren (a member of Britain's Women's Royal Naval Service). They hit it off pretty quickly and then she was on a boat back to New Zealand.
"My grandfather died when I was five or six. She lived four or five houses up the street from us and in the latter stages of her life she moved in with us. I was always really close with her."\
Heinz added: "She was an avid sports fan and a very proud Englishwoman. She never got the opportunity to get back here as much as she would have liked but she always really encouraged me and my sisters to come over and live here if we got the opportunity.
"I know she would be hugely proud of me getting this chance on Sunday.
"She was a massive sports fan, whether it was rugby, tennis, cricket. She loved it all."
But Heinz stressed he had not made the move to England in the hope of gaining a Red Rose call-up.
"I always knew I would be eligible through my English heritage but I didn't come over here assuming that I would get an opportunity," he said.
"It was about playing really well for Gloucester... If you start doing that and performing at that level then potentially you start getting opportunities higher up."
Heinz was involved in an England training camp two years ago, having played against them when they, in his words, "wiped the floor" with the Crusaders in a 38-7 tour victory back in 2014.
Now he finds himself playing for the Red Rose brigade, with Heinz, covering for regular scrumhalf Ben Youngs, also chosen as vice-captain for England's last match before coach Eddie Jones names his World Cup squad on Monday.
"I've had a little bit of experience with captaining Gloucester for the last couple of years, so it is kind of a natural role for nines and 10s I guess, because we're heavily involved with tactics through the week and decision-making on the pitch," he said.
But Heinz was still coming to terms with an England call-up that had all happened "pretty quickly".
"The main feeling is just excitement, to be honest," he said.
"Obviously, I'm a little bit older to be making my debut, but I just feel really grateful to get the opportunity and I’m excited to get out there with the lads on Sunday and rip in."