Neidhart passed away early Monday morning after suffering a medical emergency at a home in Florida.
According to the emergency dispatch audio, emergency personnel were called around 6:30 AM about a man having seizures and convulsions.
At one point, the dispatch operator says, "They think he might be Signal 7" -- which is code for a dead person.
Jim was a WWF superstar in the mid-'80s and early '90s as a member of The Hart Foundation tag team with Bret "The Hitman" Hart ... managed by Jimmy Hart.
During his legendary career, Jim was a 2-time Tag Team champion -- defeating everyone from the Legion of Doom to the Nasty Boys to The Rockers.
Neidhart also wrestled with WCW and TNA Wrestling. He last wrestled in WWE back in 2007, but has made appearances on "Total Divas."
Before he became a pro wrestler, Neidhart pursued a career in pro football -- with brief stints with the Oakland Raiders and Dallas Cowboys.
Neidhart struggled with substance abuse -- he went to rehab twice after drug-related arrests.
Neidhart is survived by his wife, Ellie, and 3 daughters including Natalie -- aka WWE superstar Natalya.
Smash from Demolition tweeted about Neidhart, saying, "It is terrible I just heard Jim Neidhart passed away. I just pray for his family to get through this.Jim was a great friend and I will really miss him."