"I feel like I've been in trade rumors for like the last six years of my career," Kapanen said Monday. "It's something I'm pretty used to, but I think coming into this year, it was going to happen. Obviously, being at home and being on waivers and looking at your phone waiting for it to ring is something new for me. But it happened and now I'm here and couldn't be happier."
Kapanen had 20 points (seven goals, 13 assists) in 43 games for the Penguins this season, but only scored one goal in his final 15 games.
The 26-year-old forward has 172 points (70 goals, 102 assists) in 364 NHL games with the Toronto Maple Leafs and Penguins.
"This year hasn't been up to my expectations," Kapanen said. "I know what I'm capable of bringing to a team when I'm at my best. I haven't been doing that as of late, so I think a fresh start is exactly what I need and to kind of prove myself and show these guys that I'm a good hockey player. Hopefully I can just help the team out."
The Blues previously traded forward Vladimir Tarasenko and defenseman Niko Mikkola to the New York Rangers on Feb. 9 for forward Sammy Blais, defenseman prospect Hunter Skinner, a conditional first-round pick in the 2023 NHL Draft and a fourth-round pick in the 2024 Draft. They then traded forwards Ryan O'Reilly and Noel Acciari to the Maple Leafs in a three-team trade that also included the Minnesota Wild on Feb. 18.
"Knowing that the number of players we lost this year, we get a player that hopefully is motivated, he should be motivated," Blues general manager Doug Armstrong said of Kapanen. "We just felt that getting a player in here at his age that has a lot to prove, under contract next year for us, so we don't have to go searching the market this year as you retool and we have a player that we know the cost, we get a good look at him. He gets a chance to play in a situation, get more ice time and prove what he is as a player.
"If it works out, we get a chance to sign him a year from now at still a young age, and if it doesn't work out, then he moves onto free agency. I don't see a lot of risk in it. We hope a lot of upside for him and for us."
St. Louis (26-28-5) is 13 points behind the Seattle Kraken for the second wild card into the Stanley Cup Playoffs from the Western Conference.
NHL.com independent correspondent Lou Korac contributed to this report