"These last three weeks have been a hard pill to swallow," he wrote. "Seeing my dreams vanish right in front of me has been extremely difficult."
Gunter, 28, explained he saw several heart specialists and was told it is too dangerous for him to continue playing football. He also said he doesn't qualify for the surgery that would have a 50-50 chance of fixing the condition.
The Jaguars signed Gunter this offseason, and head coach Doug Marrone opened up about what he brought to the team, per John Reid of Jacksonville.com:
"We really like what Rodney brings to the team, both as a player and as a person, and we think he can play multiple positions for us. We know he's a good player against the run, but we think we can get some three-down play out of him and get some pass-rush. We have high expectations for him, and we are excited about him. He is one of the pieces that we feel is going to help us defend the run and help us become a better defense."
Gunter entered the league in 2015 when the Arizona Cardinals selected him with a fourth-round draft pick, and he spent the first five years of his career on the NFC West team.
He missed just three total games in those five years, and they all came last season because of a toe injury. He finished the 2019 campaign with three sacks after posting a career-best 4.5 during the 2018 season.
The Jaguars placed Gunter on the active/non-football injury list Aug. 8.