"I think it's his ability to play the game and basically all the time making the right decisions," Tormanen said. "When the game is coming really fast he understands how to release the puck by the glass or rim it away, or make a quick turn. That's what is needed in the NHL, on a smaller rink. I think that's definitely the key aspect of his very good game."
During the NHL Scouting Combine, Heiskanen interviewed with 28 teams, showing the level of interest he's earned.
Tormanen isn't surprised NHL teams want to know more about Heiskanen.
"When he came to us in May 2016, the thinking was he would play one more year in juniors and get a few games," he said. "But right away when we saw him we knew this guy for sure would play for us and have a great chance."
Heiskanen is considered more of a reliable, poised defenseman rather than a risk-taker, but Tormanen said with Heiskanen it's more calculated gambles with the puck.
"I think he takes risks but he can foresee and solve problems before they happen," he said. "He can adjust right away to the situation. That's what I mean with his hockey sense."
Heiskanen is a left-handed shot but played the right side. That allowed him to take advantage of having the puck on the inside and away from the boards when he's handling it.
"He can make those D-to-D [defenseman-to-defenseman] passes very quickly," Tormanen said. "He knew in advance that maybe the opponent is coming, and if he's coming I'm going to deke, pass right away to the wing or skate to the middle. It doesn't matter if he turns on the backhand or the forehand."
Heiskanen's opponents also have been impressed.
Defenseman Timothy Liljegren (5-11, 188), No. 6 on NHL Central Scouting's final ranking of international skaters, has seen and played against Heiskanen with Sweden at international tournaments.
"[Heiskanen] barely makes a mistake and has real good flow to his game," Liljegren said. "He makes great passes and is good in both zones."