The 23-year-old right-hander mentioned to trainer Stan Conte after the game that he was feeling a skipped heartbeat in his chest after retiring the side in order on seven pitches in his first ninth-inning save opportunity since May 23.
Jansen was used in that situation because regular closer Javy Guerra had pitched three days in a row.
The 6-foot-5, 257-pound Jansen, converted from a catcher to a pitcher in the minor leagues a couple of years ago, was driven to nearby White Memorial Medical Center by assistant trainer Todd Tomczyk.
"It was not an emergency situation, but it was something that had to be looked at right away," Conte said. "Anytime you have an irregular heartbeat, we take it pretty seriously. So we weren't going to let him go home until we knew what was going on.
"We will go through every step to make sure that Kenley is safe to participate in everything," he added. "I mean, an elbow strain is one thing. This is something in a totally different category."
Jansen was anesthetized for about 10 minutes while undergoing cardioconversion, a process in which electricity is used to shock the heart and get it back into a normal sinus rhythm.
"We had our team physician, Dr. Mary Gendry, look at him in the training room last night," Conte said. "We did an EKG and it showed there was an irregular heartbeat that was of some concern. We felt it best that we follow up with that, so we took him to the hospital and he was seen by a cardiologist there. The question I can't answer yet — and I'll probably be able to answer in the next 24 hours — is: What do we do next?"
Conte said Jansen has no previous history of any heart-related problems, adding that the pitcher was in no distress at any time and did not experience any pain or shortness of breath.
"I don't know where this is going to go from here, because we're still less than 24 hours from this whole thing," Conte said. "It's something that happens in different people — not just athletes — and sometimes it goes away and never comes back.
"Kenley is absolutely normal now, but what we're going to end up doing now is an even more thorough work-up — EKGs, some ecocardiagrams and some special cardiac testing. That will determine where his playing status is at. Kenley's calling us and screaming at us that he wants out (of the hospital)."
Jansen has appeared in 34 games this season, going 1-1 with a 3.65 ERA and 61 strikeouts in 37 innings. He currently has a 16-inning scoreless streak over his last 14 outings since coming off the disabled list June 18, and has allowed only three hits in 51 at-bats during that stretch.
It will take at least 24 hours before the Dodgers' medical staff can determine what the next step will be for Jansen. He was scheduled to remain in the hospital overnight again so that a more thorough work-up can be done on him to help determine what may have caused the episode.
"Whether this can be triggered by stressful situations or whatever, he didn't seem to be in any more stress than he had been before," Conte said. "We don't necessarily see a cause-and-effect relationship between this and the stress of a major league baseball game, but we'll investigate a lot of different things."
Conte said his last such incident with a player's irregular heartbeat involved former Dodgers reliever Joe Beimel, who was back on the mound two days after getting his heart shocked back into its normal rhythm.
"Joe may be the exception to the rule," Conte said. "Essentially, it's rebooting the heart. The rhythm of your heart is determined electronically. So you have to reset it. Most times, it converts — and this time it did. So now you just monitor it to make sure it doesn't go back."