Blair, 50, is "fit, fine, in good spirits and 100 percent recovered," his official spokesman told reporters, a day after the prime minister was rushed to a hospital for electrical stimulation to regulate the heartbeat.
Doctors said the episode did not raise any question about Blair's fitness to continue his grueling job.
It was the first known health scare for the fit and youthful looking leader, who has had a stressful year battling continuing criticism of his decision to go to war in Iraq and turmoil within the governing Labor Party over domestic issues.
Told to take it easy for 24 hours, Blair was in his office working but canceled an appearance in the House of Commons on Monday. His spokesman said, however, that Blair would hold his usual meeting with Queen Elizabeth II on Tuesday and answer questions in the Commons on Wednesday.
"He's not going at full throttle today, but he will be doing everything tomorrow that he has to do," his spokesman said, briefing reporters on condition of anonymity. He added that Blair would have a medical checkup within two weeks.
While it appeared unlikely that Blair would have to leave office because of a health problem, political commentators suggested the incident might make the two-term prime minister more willing to yield power at the next election, which must occur by 2006.
Speculation has been rife for years over when Blair would step aside as Labor leader. Britain's Chancellor Gordon Brown has been waiting in the wings for years.
Asked whether the problem had caused Blair to reflect on his future, the spokesman said: "He's getting on with the job. His appetite for the job is the same today as it was this time last week."
Blair was spending the weekend at Chequers, his official country residence, when he felt ill, his office said. He was first taken to a local hospital, then to London's Hammersmith Hospital.
"There it was established he had an irregular heartbeat and a cardioversion was administered to regulate it," Blair's office said. Cardioversion is the use of an electrical stimulus to restore a normal rhythm.
Blair was "sedated" for 20 minutes during the procedure, said the spokesman.
National Security Adviser Condoleezza Rice said President Bush had not spoken to Blair, his close ally, since the episode.
"We were very glad to hear, obviously, that the prime minister is doing well," Rice said at a news conference in Bangkok, Thailand, where the president was meeting with Asian leaders.
Irregular heartbeats are most common in the elderly, but a British Heart Foundation report from 1999 said the condition affects 3.9 percent of men aged 45-55.
Sir Charles George, medical director of the British Heart Foundation, said triggers could include stress, too much caffeine or some minor abnormality which had existed from birth. "The evidence shows that these things happen out of the blue," George said.
"There is no real reason for him to stop playing tennis or to stop being prime minister, based on this," said Dr. Duncan Dymond, a consultant cardiologist at St. Bartholomew's Hospital in London.
The Guardian newspaper reports that were Blair to be incapacitated or leave office, there is no clear process for the succession of power.
In Britain's parliamentary system, Blair is prime minister because he is the elected leader of the party that holds the most seats in the House of Commons, the Labor party. Were Blair to leave office, Deputy Prime Minister John Prescott would likely take over while the Labor party selected a new leader.
But the Guardian reports that the new leader would face calls to hold a new election to allow the voters to weigh in. Elections in the UK are not scheduled for certain dates but must occur at least once every five years, either at the behest of the governing party or the Queen, if she dissolved Parliament.
Two 20th Century prime ministers died in office: Henry Campbell Bannerman in 1908 and Andrew Bonar Law in 1923. Two others left office early due to poor health, Anthony Eden in 1957 and Henry Macmillan in 1963.
Blair's father Leo died from a stroke. But according to the Times of London, Blair exercises regularly and has not smoked since his wedding day in 1980.