Shane del Rosario, 30, died at a hospital in Newport Beach, Calif., nearly two weeks after suffering cardiac arrest.
Teammates Ian McCall and Carla Esparza confirmed the news on Twitter.
The UFC recently confirmed the news and released a statement.
The Ultimate Fighting Championship mourns the tragic loss of heavyweight competitor Shane Del Rosario, who has passed away at the age of 30. Del Rosario suffered a heart attack on Tuesday, Nov. 26 as a result of what doctors believe to be a congenital heart disorder, according to his manager Jason House.
The entire organization sends its deepest condolences to Shane's family and friends.
According to a Sherdog.com report, McCall, del Rosario's roommate, discovered del Rosario unconscious on the floor of their Laguna Niguel residence on Nov. 26. McCall administered CPR and contacted 911, who sent an ambulance which transported him to the hospital.
There was online confusion on Thanksgiving Day after a published report indicated del Rosario died, but del Rosario's manager, Jason House, clarified the situation, saying he was still alive but "needed a miracle."
A lifelong resident of Orange County, Calif., Del Rosario got into mixed martial arts after graduating from the University of California at Irvine, where he earned his bachelor's degree in psychology.
Del Rosario, who also competed in kickboxing, made his MMA debut in 2006 and won his first 11 professional fights, all via finish. This culminated in his biggest career victory, a first-round finish of Lavar Johnson on Feb. 12, 2011, in E. Rutherford, N.J. The bout was an alternates match in the Strikeforce Heavyweight Grand Prix tournament.
His life changed, however, two months later. Del Rosario was the victim of a drunk driving accident, as an inebriated driver slammed into his car from behind while del Rosario was stopped at a red light. Del Rosario was out of action for more than a year. As he readied for his return last year, del Rosario spoke about putting his frustrations in perspective.
"I had some dark times and it really sucks not doing what you want to do, but I put it all in perspective," del Rosario said. "My thing isn't all that bad. Other people are going through a lot of hard stuff."
Del Rosario returned to competition in 2012 and fought twice, first losing to Stipe Miocic at UFC 146, then to Pat Barry in December.
A member of Team Oyama in Irvine, which includes McCall and Esparza, del Rosario was scheduled to fight Guto Inocente at UFC 168, but recently pulled out with a rib injury.