"We're having to evaluate [him], and it may be tough," Fisher told reporters. "It's nothing he can control or anybody can control. It's something we found, so it's a safety issue."
The 22-year-old Mavety started eight games -- five at left guard and three at right tackle -- as a redshirt junior for the Seminoles last season but did not play in the Peach Bowl.
Fisher said Thursday that Mavety, who was affected by the cardiac issue toward the end of last season, is out indefinitely.
Mavety is one of 10 FSU players who won't participate in spring drills, which begin March 16. That list also includes quarterback Sean Maguire, who is recovering from ankle surgery.