Heiskanen, a defenseman, was taken by the Dallas Stars with the No. 3 pick at the 2017 NHL Draft. He was a key to the Stars' run to the Stanley Cup Final in 2020 with 26 points (six goals, 20 assists), the most by a defenseman in the postseason since Brian Leetch of the New York Rangers had 34 in 1994.
The native of Espoo, Finland, entered the NHL to start the 2018-19 season and quickly showed why the Stars had valued him so highly. He played all 82 games, finishing fifth on the Stars with 33 points (12 goals, 21 assists) and fourth with four game-winning goals. He scored his first NHL goal Oct. 25, 2018, against the Anaheim Ducks; at 19 years, 99 days, he was the second-youngest defenseman to score in Stars/Minnesota North Stars history (Ron Meighan, 18 years, 207 days).