The Predators, Ottawa Senators, Columbus Blue Jackets and Vegas Golden Knights were all kept busy with deals as general managers around the league look to retool their rosters ahead of the playoffs, entry draft and offseason free agency.
Nashville has its sights set on a deep run this postseason after acquiring the 30-year-old Simmonds, who is in his eighth season with the Flyers after spending his first three seasons with the Los Angeles Kings.
Simmonds has 16 goals and 11 assists in 62 games this season. In 584 games with the Flyers, he scored 203 goals, 175 assists and 784 penalty minutes.
Philadelphia hasn't made it past the first round of the playoffs since 2011-12 season. Hartman, 24, has 10 goals and 10 assists in 64 games this season.
The Ottawa Senators also tried to bolster their team for a late season run by sending forward Mark Stone and Tobias Lindberg to the Golden Knights with Ottawa getting defenceman Erik Brannstrom, forward Oscar Lindberg and a second-round draft pick from Dallas.
Vegas then quickly agreed to a contract extension with Stone. The deal will be for eight years and worth an average of $9.5 million per season, the US media reported.
"Obviously, there's some mixed feelings," Stone told Canadian sports network TSN. "I'm so excited to be joining the team. Just seeing what they did in the playoffs was unbelievable. But I enjoyed my time in Ottawa. I love the city. So many great people here."
The deal means that the Senators have parted with their top three scorers in a matter of days. The Senators also sent Matt Duchene and Ryan Dzingel to the Columbus Blue Jackets in separate deals.
Also, Brendan Lemieux, the son of former NHLer Claude Lemieux, was traded along with two draft picks from the Winnipeg Jets to the rebuilding New York Rangers for centre Kevin Hayes.
The Blue Jackets gave the appearance of being busy at the deadline acquiring several journeymen players, but they might have had to sacrifice the future to do it, giving up two solid prospects and a couple of top draft picks.
Columbus is now left with just two draft picks this June (third and seventh round) and no picks in the first two rounds.