The defenseman, who turned 22 on Sunday, could have become a restricted free agent July 28. He scored 27 points (eight goals, 19 assists) in 55 games this season and led the Stars in average ice time per game (24:58).
"I really love the city of Dallas, love my teammates, the whole organization, so that's why I wanted to be here in Dallas," Heiskanen said Monday. "Of course, I think we have a great team and a great chance to win the Stanley Cup. That's why I wanted to be a Dallas Star for a long time.
"It's huge contract and great for me."
Heiskanen said any outside pressure to live up to a long-term contract will not be a distraction. Dallas (23-19-14) finished fifth in the eight-team Discover Central Division this season and did not qualify for the Stanley Cup Playoffs.
"I don't think about that too much, what other people are talking about," Heiskanen said. "There's always some comments or something but I don't really care what people outside are thinking. I just do my stuff, play my game, have fun, try to be better every day.
"It feels great to get this done. Of course there is a lot of work to be done and we're very motivated to get back on the ice. It is very exciting to be a part of what (general manager) Jim (Nill) and his staff are building, and it's important to reward them for the trust they've shown with this long-term commitment."
Selected by Dallas with the No. 3 pick in the 2017 NHL Draft, Heiskanen has scored 95 points (28 goals, 67 assists) in 205 regular-season games and 30 points (eight goals, 22 assists) in 40 playoff games.
"He wanted to be a Dallas Star for life," Nill said. "Dallas is his home, he loves the team, he loves his teammates and he just wants to know that he's compensated fairly, and that he just wants to go play hockey.
"He's a smart kid, he's a very respectful kid who respects the game, he respects his teammates and respects the fans and everything that goes with it. Really, he's just touching the early parts of his career and there's so much more room for growth. If you look through the careers of top defensemen, Norris Trophy-winning defensemen, who come through the NHL, where his career is at compared to them, he's ahead of many of those people. He's got a lot more room to grow and continue to improve, but it's just really experience and gaining time."