His announcement however had the opposite effect -- sparking frenzied speculation about how long he can go on and whether he was now blocking his powerful No. 2, finance minister Gordon Brown, from taking over.

Blair, 51, called the procedure to correct recurrent heart palpitations "routine." Aides said he would be back at work early next week after an overnight stay in a London hospital.

"I feel fine," he told reporters as he left his Downing Street home for hospital, smiling and waving.

Blair's renewed heart problems surprised Britons, with many blaming the toll of such a grueling job and the flak he has taken over the Iraq war.

But it was Blair's accompanying announcement -- that he wanted to serve a full third term but would not contemplate a fourth -- that really sent UK politicians into a spin.

Blair is expected to call and win an election in May 2005.

"Do I wish to serve a full term? The answer to that is 'yes.' Do I want to go on and on and on? The answer to that is 'no,"' Blair said.

The announcement, timed for the final day of his Labour Party conference, seemed to rule out a much-speculated early handover to Brown, widely viewed as the heir-apparent.

But with a full third term possibly taking Blair to 2009, many wondered if that could be too long for Brown, 53, to wait. Some Brown supporters say Blair has reneged on a supposed deal made back in 1994 for a handover of power in a second term.

Analysts said a leadership race was now firmly on the horizon, with Blair losing authority in a third term.

"I think he would become a progressively lamer duck," analyst Peter Kellner said. "I would expect him to resign well before the end of the next term."

But Blair insisted Brown would make a "superb" future leader even after a third term for him. "I don't think it rules Gordon out in any shape or form at all," he said.