Jim Harbaugh endured a concerning moment on the sidelines early during the Los Angeles Chargers' 23-16 Week 6 win over the Denver Broncos.

Harbaugh began the Week 6 game coaching the Chargers on the sideline before heading to the medical tent without explanation. He briefly left the field and went back to the locker room in the first quarter, leaving many to wonder whether the 60-year-old was OK.

Eventually, Harbaugh emerged from the locker room and took back the coaching reins from the interim coach, defensive coordinator Jesse Minter, with just over 7 minutes remaining in the first quarter. Harbaugh finished the victory with no further issues.

What happened to Harbaugh? The veteran coach explained his medical situation during his postgame news conference.

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What is Jim Harbaugh's heart condition?

Harbaugh explained to reporters that he has a heart condition that acted up during the Chargers' Week 6 game against the Broncos.

"It's called atrial flutter," Harbaugh said after the game. "I got into an episode [Sunday]."

That episode prompted Los Angeles' medical staff to examine Harbaugh and eventually take him back to the locker room. There, they gave him intravenous (IV) fluids and performed tests to ensure that the coach was healthy.

"Did an [electrocardiogram], and they said it was back to the sinus rhythm," Harbaugh told reporters. "And I said I feel good, so I got back there on the field."

Harbaugh reiterated he was feeling good during his postgame news conference. He also revealed he planned to follow up with a cardiologist on Monday after his episode.

"Trust the doctors," Harbaugh said. "It's the heart, so you take it seriously, right? Trust the doctors."

Monday Ravens coach John Harbaugh said his younger brother was feeling better and had dealt with the issue before.

What is atrial flutter?

Atrial flutter is a type of heart rhythm disorder during which the heart's upper chambers beat faster than its lower chambers. This causes the heart to beat in a sped-up but consistent pattern, as the Cleveland Clinic details.

"A normal heart rate is 60 to 100 beats a minute when you’re at rest," reads the Cleveland Clinic website. "Atrial flutter can make your heart’s upper chambers beat 250 to 350 times a minute. This causes your lower chambers to beat fast as a response, commonly as fast as 150 beats a minute or more."

Atrial flutter is caused by abnormal electrical signals in the heart. There is no cure for the condition but it can be treated with medicines and surgical procedures meant to correct the heartbeat.

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Atrial flutter symptoms

Atrial flutter causes the heart not to work as efficiently as it should and can lead to symptoms including:

• Dizziness
• Shortness of breath
• Lack of energy
• Heart palpitations
• Fast pulse
• Lightheadedness
• Chest pain
• Passing out

It can also weaken the heart muscle, create blood clots, and cause blood pressure drops that can lead to heart failure, per the Cleveland Clinic. Thus, it is a serious condition that must be monitored.

AFib vs. atrial flutter

Atrial flutter is similar to atrial fibrillation, more commonly known as "AFib," but there is a key difference. According to Johns Hopkins Medicine, AFib does not have an organized rhythm, as the upper ventricles beat rapidly and chaotically, often more than 400 times per minute.

Atrial flutter sees the heart beat rapidly but in a consistent pattern.

Contributing: Tyler Dragon, USA TODAY Sports