Federal Judge Catherine Eagles did not disclose the exact nature of Edwards' illness Friday or what procedure he needed. However, she said the two-time presidential candidate had "three episodes" and indicated his condition could be life-threatening if left untreated.
A cardiologist for the 58-year-old ex-North Carolina senator wrote two letters about his condition to Eagles, who talked about them during a hearing to consider whether the trial on six felony and misdemeanor counts should begin this month. Eagles said jury selection will now start March 26, at the earliest.
Edwards is taking medication and is scheduled to undergo a procedure in February from which it will take several days to recover, Eagles said. She did not describe what the episodes involved or if the procedure would require unclogging arteries or other common treatments. The doctor's letters and other medical records have been kept under seal by the court.
"The public has an interest in a speedy trial," Eagles said from the bench. "Ordinarily, I would try to manage something like this. But clearly there are some limitations on Mr. Edwards due to real and serious health issues."
His doctor had recommended he not drive or travel, but at the judge's request, Edwards was in court. He didn't appear to have any outward signs of illness, though he was without his usual quick smile or bounce in his step.
The trial has already been delayed twice, including a continuance granted so Edwards could attend his eldest daughter's wedding.
Prosecutors took no position on whether the judge should grant the delay due the defendant's health condition, but said they were ready to try Edwards. He is accused of concealing nearly $1 million in cash and checks from wealthy donors used to help hide his pregnant mistress during his 2008 White House run.
Edwards's legal team and spokespeople have been mum about his condition since his diagnosis last month, declining repeated requests for comment on his condition, including after the hearing.
Known for being telegenic Edwards had customarily entered the federal courthouse through the public entrance, where a group of reporters and cameramen assemble. But on Friday, he took steps to slip through unnoticed. A court security officer indicated he had come and gone through a back door.
Two years ago, Edwards confessed he fathered a baby born to his ex-mistress. He had long denied the girl, Frances Quinn Hunter, was his, even after he admitted cheating on his wife with the child's mother, Rielle Hunter. Hunter had been hired before Edwards' 2008 White House campaign to shoot behind-the-scenes video of him.
Edwards' confession came ahead of the release of a book by former aide Andrew Young. The book described how Edwards worked to hide his paternity with the help of his married aide.
Shortly before the 2008 presidential primaries began, Young stepped forward to claim that he -- not Edwards -- was the child's father. But there were suspicions at the time that the fiercely loyal aide was taking the fall for his boss.
The child was conceived in mid-2007, while Edwards was running for the White House, and around the time he was renewing his vows after 30 years of marriage.
After Edwards admitted fathering Hunter's child, Elizabeth Edwards separated from him and filed for divorce. She died in December 2010 from incurable breast cancer that was first diagnosed in 2004, a day after the Democratic ticket that included John Edwards as the vice presidential candidate lost to George W. Bush.
The Edwardses were law school sweethearts who married just days after they took the bar exam together in the summer of 1977. They had four children together, including a son who died at age 16. Although the couple had separated, John Edwards was at her side around the clock as her health deteriorated. He did not speak at her funeral.
Edwards made millions as a trial lawyer before beginning his political career with a successful 1998 Senate campaign.