"I don't know if concern's the right thing but we're getting him checked out. I'm sure it was a scary thing for Scott with the elevated heart rate," Philadelphia general manager Paul Holmgren told reporters at the Flyers' practice facility Sunday.
Hartnell noticed some twitching in his arms after the second period of an exhibition game in Detroit and trainers checked his heart rate and found it was still higher than it should have been.
The 29-year-old did not return to the game and won't play in Monday's preseason game.
"They checked his heart rate and it was elevated more than it should have been after a period of time after play had stopped. So they held him out and we'll just continue to monitor and run some tests on him," Holmgren said.
Holmgren said it took an "abnormal" amount of time for the heart rate to return to normal and that he is hopeful Tuesday's examination by a cardiologist will allow them to "get to the bottom of it."
Hartnell, who did not skate Sunday, did not allude to the incident when he met with reporters Sunday.
"Just a maintenance day, just a little sore," he said.
Scott Burnside covers the NHL for ESPN.com.