The 23-year-old Jansen complained after the game of a "flutter," according to manager Don Mattingly. He mentioned it to trainer Stan Conte after his seven-pitch outing resulted in his second save of the season. After being administered an EKG, Jansen was taken to a local hospital, where he is expected to remain until Thursday.
Mattingly said the condition was first noticed in a physical exam during Spring Training and Jansen will continue to be monitored at the hospital, but added that it is not expected to keep Jansen from continuing his career.
"It didn't sound that alarming," Mattingly said. "Talking with Stan, they were talking about him possibly pitching Saturday."
Conte said Jansen approached him after the game, saying he felt he had a "skipped heartbeat." He took the EKG at Dodger Stadium before Conte decided to proceed with caution.
"We felt it best to follow up immediately and we took him to White Memorial, where he was seen by a cardiologist," Conte said.
While there, Jansen had a cardio conversion to get rhythm back to his heartbeat by shocking it with electrodes. Conte said Joe Beimel received the same treatment a couple years ago and pitched two days later.
"His heartbeat is regular now and everything is absolutely normal," Conte said. "We'll do even more testing to see what triggers this. After we find that out, we'll determine his playing status."
The reasons for the irregular beat were unknown, Conte said. He wasn't sure whether stress could be a cause, but he didn't notice Jansen feeling at all stressed. He said it could be a number of factors, such as food or drink.
After a shaky start to the season and a three-week stint on the disabled list for a sore right shoulder, Jansen has been one of the most effective relievers in the game over the past six weeks.
Since returning from the disabled list on June 18, he has struck out 26 over 16 scoreless innings, holding the opposition to a .059 batting average (3-for-51).
Ken Gurnick is a reporter and AJ Cassavell is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.