Los Angeles has begun a four-game set against the Colorado Rockies, who play at altitude in Denver.
Manager Dave Roberts stated that Jansen will be evaluated further but is in stable condition, according to Pedro Moura of The Athletic, who also noted the reliever had suffered a similar ailment in Colorado six years ago.
"Any time you're talking about the heart, we obviously have to be very careful with it," Roberts told reporters, according to MLB.com's Anne Rogers. "And then we're talking about altitude, so that's why we wanted to be proactive and get him back there. We're holding out hope that it's not too serious, but talking to the trainer right now, his mood is fine, you wouldn't know the difference, and once we get more testing, we'll know more."
The Dodgers won the opener of the four-game set against the division-rival Rockies by a score of 8-5.
Over 54 1/3 innings out of the bullpen this season, Jansen has authored a 2.15 ERA and 3.11 FIP, while notching 32 saves.