Tony Blair erupted in anger after Michael Howard taunted him about the numbers of cancelled NHS operations, during Prime Minister's Questions.
Mr Blair said if the claim was true, it was 'unacceptable'
The Tory leader cited the case of 69-year-old Margaret Dixon who had her operation cancelled seven times.
Mr Blair said it was not fair to use one bad experience to undermine the basic principles of the NHS.
Mrs Dixon said the NHS may have improved over the last eight years, but "it's not done any good for me".
The pensioner's case was raised as Mr Howard challenged Mr Blair to explain why 67,000 people had had their operations cancelled, despite all the investment Labour had made in the NHS.
He said the pensioner, who lives just outside Warrington, is "in constant pain and desperately needs an operation".
"Because she has a weak heart, she's been told that her chances of surviving that operation is less than 50:50," he said.
"On seven separate occasions she's been given a date for the operation, been prepared for it and said goodbye to her family in case she didn't survive.
"On each of those seven occasions, her operation has been cancelled.
"She's praised the doctors and the nurses, but can you explain how after eight years of your government, all the money you have spent on the NHS and all the promises you've made, this can happen in Britain today?"
Mr Blair said he had only been informed of the case by fax a few minutes before prime minister's questions, but added: "If it is as you describe, it's completely unacceptable.
"What I do think is quite wrong is to take a case ... and try and make what I believe is an exception into the rule in our National Health Service."
But Mr Howard hit back that Mrs Dixon was "not an isolated case".
Mr Blair said the numbers of cancelled operations were "a very small proportion" of the overall numbers.
He attacked the Tories for opposing investment in the NHS, which, he said, had produced more nurses, wards and new hospitals.
Mr Blair's spokesman said later that the proportion of cancelled operations had varied very little over the years.
In an interview with BBC Radio 4's the World at One programme, Mrs Dixon, who was due to have an operation on her shoulder at Warrington General Hospital, said she had been happy to have her case highlighted in the Commons.
"The NHS may have improved in the last eight years. The area where I really require it, it hasn't and it's not done any good for me," she said.
Mrs Dixon was happy to have her case highlighted in the Commons
The hospital at the centre of the row, the North Cheshire Hospitals NHS Trust, later said in a statement it "very much regrets this particular patient's operation has not yet taken place and is endeavouring to reschedule it for a date in the near future".
Mrs Dixon, who suffers from kidney, heart and lung problems, needed a high dependency unit (HDU) bed.
The hospital said it was "very unfortunate" there had been unforeseen demand on HDU each time Mrs Dixon had been in hospital.
The Cheshire and Merseyside Strategic Health Authority is now considering a new development to increase the Trust's critical care capacity, the statement said.
In the Commons, Mr Howard said NHS investment was being ploughed into bureaucracy and managers instead of frontline staff - a charge Mr Blair denied.
Mr Blair said the Tories wanted to take £1bn out of the NHS for a voucher system which would give people who go privately half of the cost of their operation - a charge later denied by the Tories.
Amid rowdy scenes, Mr Blair demanded: "Don't these Tories ever learn? Stand up and tell us how an old age pensioner, living on the pension is going to be able to afford a hip operation?"
Accusing Mr Blair of "simulated anger," Mr Howard claimed that numbers of people who have to pay for their operations had tripled to 250,000 people a year under Labour.