The 20-year-old defenseman leads the Stars in time on ice at 24:57, is second in scoring with 17 points in 24 games, leads the team at plus-13, and is second in blocked shots at 39.
"He's the engine that makes it go," Montgomery said matter-of-factly. "He just does."
Part of that is the fact Heiskanen has been given a bigger role in his second NHL season while John Klingberg has battled a lower-body injury, and part of it is that he's just that good. Heiskanen was taken third overall in the 2017 NHL entry draft, so he definitely has a pedigree, but he also is a skilled defenseman who started working out of a defensive base and is now adding offensive skills to his game.
Video: VAN@DAL: Heiskanen buries one-timer off give-and-go
Heiskanen was not a finalist for the Calder Trophy given to the rookie of the year last season, in part, because he tallied "just" 33 points (12 goals, 21 assists) in 82 games. But those who watch him on a regular basis say that his ability to see the game, anticipate plays, and keep his team in a good place is incredibly underrated.
The Stars have battled some of the best players in the league in recent weeks -- facing the likes of Nathan MacKinnon, Patrik Laine, Johnny Gaudreau and Elias Pettersson -- and Heiskanen usually has had the assignment of trying to shut them down. But maybe the most impressive feat was when assistant Rick Bowness tried to get Heiskanen out against Connor McDavid as much as he could when Dallas played on the road against the Oilers last week. McDavid finished with three assists, but they didn't come against Heiskanen. The sophomore blueliner had a goal, an assist, and seven shots on goal in the game while finishing plus-1 in a 5-4 overtime win.
"He went head-to-head (with McDavid) and we had him with 10 chances for and one against per our scoring chances," Montgomery said. "That's an elite game."
Heiskanen was on the ice for a goal against that looked like his fault early in the Oilers game, but Montgomery said further film study said it was a fluke.
"He was really good the entire game," Montgomery said. "He had the one goal where the puck went off a shoulder as he tried to get it out. I don't think that was a mental mistake. He was dynamite from start to finish that game."
Video: DAL@EDM: Heiskanen nets Benn's feed
Even if he makes a mistake -- as he did Saturday in overtime against Chicago -- Heiskanen said he doesn't really let it bother him. While he knows his assignments and knows when he doesn't complete them, he sees no value in fretting.
"I don't worry about it, I don't know why," he said. "No one is perfect, everybody makes mistakes. I just try to forget it and try to do my best."
Pressed on the subject, Heiskanen said: "I definitely know when I make a mistake and then try not to do it again. I think that's it, just try to learn from your mistakes. It's small things, but that can help when you go through that. … Maybe a little bit I want to get it back, maybe.
"I just want to be better and better. I always want to get better."
How he does that still is a bit of mystery to those who watch. Heiskanen certainly has special skills in that he is one of the best skaters on the team and also has quick hands that allow him to both create and defend well. However, it's his vision of the game and hockey IQ that really set him apart.
Video: DAL@CBJ: Radulov, Heiskanen team up for goal
"For a guy that is as humble and quiet as he is to have that inner confidence is impressive," said forward Tyler Seguin, who explained that he had to balance confidence with lessons from older players.
"I think I got my footing because I was such a cocky kid. I had an arrogance, a confidence, and that's what pushed me," Seguin said. "His is just his brain and his skill taking over. I had to be humbled to get to where I am. Miro, he came in with just the right balance."
Jamie Oleksiak, who has had to fight to find a place in the league after seven seasons, said he too sees something special and different in how Heiskanen handles the pressure of being a defenseman.
"It kind of drives me crazy a little bit, he's always got a straight face," said Oleksiak, who has been partnered with Heiskanen in recent games. "I'll look over and try to read his face or his eyes, and it's really hard to read. We'll be in the middle of a game that's pretty intense and he's just like it's a regular old practice.
"He's always just Miro. He's consistent, he's reliable, you can always just rely on what he's going to be like every day."
Video: DAL@STL: Heiskanen scores from along the goal line
Oleksiak said he is as impressed with Heiskanen's defensive play as his offense.
"He's got great offensive tools, that's obvious, but his maturity and the way he uses his stick is also very impressive," Oleksiak said. "He's never doing too much. He picks his spots, but he's not risky with the puck. He's very good with his stick positionally, he's solid defensively, he's not a liability."
So how does he do it? Heiskanen said he definitely works on all elements of the game, it's just that he does it in his head. He said that he takes lessons taught by Bowness and then uses practice and down time to come up with a plan on the ice rather than talking things out.
"Bones always gives me tips, so that helps," he said. "But I like more just thinking about it myself. I listen and then I try to make the plays on the ice. Mostly, I just think in practice and then at home, and then when I get to the game I try to make the plays on the ice."
So far, that plan is working great.
Video: MTL@DAL: Heiskanen finds the empty net for goal
"I think it's first his mind, yes, but then you factor in the hands and the subtleties," Montgomery said. "He does it all. He's blessed."
In fact, he might start drawing interest as a Norris Trophy candidate later in the season. If he needs a campaign manager, Montgomery would be a good place to start.
After Heiskanen made a few dazzling plays in a 6-1 win over Vancouver on Tuesday, Montgomery shrugged and said: "I didn't think he could go to another level and he did again. It's unreal. We were sitting there like, "Wow." What you guys (the media) do; that's what we (coaches) do. It's pretty amazing, because we deal with these high-level athletes all of the time, but he is at a level that you don't see very often."
So much so that Heiskanen really could be the engine driving one of the best streaks in franchise history.
"I don't think Miro gets enough credit for how good he is," Montgomery said. "He's an elite, elite player in this league."
Top photo: Sean Berry / Dallas Stars
This story was not subject to the approval of the National Hockey League or Dallas Stars Hockey Club.
Mike Heika is a Senior Staff Writer for DallasStars.com and has covered the Stars since 1994. Follow him on Twitter @MikeHeika, and listen to his podcast.