The surgery will be performed early this week at a hospital in Charlotte, N.C., where Fox has an offseason home. He was in Charlotte on Saturday, as the Broncos have a week off, and was taken to the hospital after experiencing light-headedness and dizziness on the golf course.
The surgery will take place either Monday or Tuesday.
In a written statement, the Broncos said Fox, 58, was advised by doctors months ago that his defective aortic valve would need to be replaced following the 2013 season. As part of his trip to North Carolina over the bye week, he had a preoperative appointment Thursday and his doctor told him to seek medical attention immediately if he felt any discomfort.
The Broncos, who are 7-1, have yet to name a temporary replacement for Fox, but defensive coordinator Jack Del Rio is expected to be named interim coach. He has the most head-coaching experience among the assistants, having coached the Jacksonville Jaguars from 2003-11.
In a statement released by the team, Fox said: "I sincerely appreciate all of the support from friends, Denver Broncos fans and so many around the league today.
"Although I am disappointed I must take some time away from the team to attend to this pre-existing health condition, I understand that it's the the right thing to do. I have great confidence in our coaches and players, who are fully committed to our goals.
"I look forward to returning to coaching as soon as possible."