The Los Angeles Chargers were without head coach Jim Harbaugh early Sunday afternoon in their 23-16 victory over the Denver Broncos.

Harbaugh was seen minutes before their game started at Empower Field at Mile High in Colorado, walking from the sideline into the team’s blue medical tent to get checked out. It was unclear at the time what was happening and Harbaugh walked back to the locker room minutes later. As a result, he missed the start of the match.

A few minutes into the game, the Chargers then confirmed that Harbaugh was dealing with an illness and was questionable to return. Defensive coordinator Jesse Minter stepped in, serving as the team’s interim head coach in the meantime.

Harbaugh’s brother, Baltimore Ravens head coach John Harbaugh, abruptly ended his press conference after also being informed of the situation in Denver. John spoke after the Ravens’ 30-23 win over the Washington Commanders, leaving to call his brother and check in, according to Jeff Zrebiec of The Athletic. It is unclear whether he got through or was able to talk to Jim.

Just past the midpoint of the first quarter, Harbaugh returned to the sideline and took over again. He returned just in time to see quarterback Justin Herbert also throw a 38-yard touchdown pass to Kimani Vidal, putting the Chargers up 10–0.

Harbaugh told CBS that he was dealing with an arrhythmia, an irregular heartbeat. Harbaugh said he’s been dealing with it for “some time.” He said after the match that he experienced an atrial flutter, where the abnormality causes the upper chambers of the heart to beat too fast.

“I started an episode on it today,” Harbaugh said. “The doctors examined me and it came back into sinus rhythm, a normal rhythm, so I came back.”

Harbaugh said he will have a follow-up appointment with doctors on Monday to determine his status and the severity of his arrhythmia on Monday.

Harbaugh is in his first season with the Chargers this fall after a nine-year stint at Michigan, which he ended with a national championship in January. It is his first job in the league after leading the San Francisco 49ers for four seasons from 2011 to 2014. Harbaugh said he experienced a similar arrhythmia during a “Monday Night Football” game with the 49ers. The 49ers defeated the Chicago Bears that night, a game Harbaugh said he will always remember.

“I’m 2-0 with arrhythmias,” Harbaugh said with a laugh.

After their fast start, the Chargers held on late to take the seven-point victory in Denver on Sunday afternoon. They scored 23 unanswered points to start the game, thanks to a pair of field goals from Cameron Dicker and a four-yard touchdown run from JK Dobbins after Vidal’s touchdown, before the Broncos finally put points on the board. Justin Herbert went 21 of 34 for 237 yards with a touchdown pass. Dobbins also finished with 96 yards and a score on 25 carries. The win snapped a two-game losing skid for the Chargers and pushed them to 3-2 on the season.

Bo Nix went 19 of 33 for 216 with two touchdowns and an interception in the loss to the Broncos. Both of his touchdown passes came in the fourth quarter. Courtland Sutton, who finished with 53 yards on four catches, caught one of them with a wild one-handed grab in the back of the end zone.

The Broncos, who had won three straight on Sunday, are now 3-3 on the season.