The Vatican has acknowledged that Pope Benedict XVI has had a pacemaker for years, one day after his resignation.
Vatican spokesman Federico Lombardi reiterated that Pope Benedict was not stepping down because of any specific illness.
The Pope’s last public appearance will be his final mass in Saint Peter’s Square on February 27, Federico Lombardi said.
The pontiff would have no role in the running of the church after his resignation, he added.
The unexpected development – the first papal resignation in nearly 600 years – surprised governments, Vatican-watchers and even the Pope’s closest aides.
Cardinal Joseph Ratzinger became Pope Benedict XVI in 2005 after John Paul II’s death.
In theory there has never been anything stopping Pope Benedict or any of his predecessors from stepping aside.
Under the Catholic Church’s governing code, Canon Law, the only conditions for the validity of such a resignation are that it be made freely and be properly published.
But resignation is extremely rare: the last pontiff to step aside was Pope Gregory XII, who resigned in 1415 amid a schism within the Church.
According to a report in Il Sole 24 newspaper, the Pope had surgery to replace a pacemaker just under three months ago.
At a news conference at the Vatican, Father Federico Lombardi confirmed that the batteries in the pacemaker, which had been fitted several years ago, had been replaced in the routine operation.
“That hasn’t affected his decision [to resign] in any way and simply he felt that his strength was diminishing with the advancement of age,” he said.
Earlier the pontiff’s brother, Georg Ratzinger, said the Pope had been advised by his doctor not to take any more transatlantic trips and had been considering stepping down for months.
“When he got to the second half of his 80s, he felt that his age was showing and that he was gradually losing the abilities he may have had and that it takes to fulfill this office properly,” he said.
He said the resignation therefore was part of a “natural process”.
The Vatican now says it expects a new pontiff to be elected before Easter.
Father Federico Lombardi said the Pope would continue with his diary as usual until the day he officially retires on February 28.
He is due to officiate at an Ash Wednesday service at the Vatican.
“The last general audience [on 27 February] will be held in the square since a lot of people will come,” AFP news agency quotes Father Lombardi as saying.
After that the Vatican has said he will retire to the papal residence at Castel Gandolfo before moving into a renovated monastery used by cloistered nuns for “a period of prayer and reflection”.
“He’ll stay in Rome and will certainly have some duties and of course will continue to educate himself intellectually and theologically,” said Georg Ratzinger.
“Where he’s needed he will make himself available, but he will not want to want to intervene in the affairs of his successor,” he said.
At 78, Cardinal Joseph Ratzinger was one of the oldest popes in history at his election.