Mr Heseltine, 64, was taken from his home, Thenford Manor in Northamptonshire, to hospital in Banbury with pains in his arms early yesterday morning. Conservative Central Office later announced that he had decided not be a candidate in next month's election to succeed John Major, but said there was no question of him standing down as an MP.
His wife Anne said she was "delighted" that he would not be standing. "He has not had a heart attack," she said. "They are doing tests and are keeping him in for a rest for a day or two. He is very chipper. They are having to strap him to the bed to keep him there."
Mr Heseltine was the bookmaker's favourite for the Tory leadership, with William Hill quoting him at 7-4.
His illness, though not immediately life-threatening, has written the final chapter in a remarkable political career which he had always hopedwould end in Downing Street.
The man who precipitated the downfall of Margaret Thatcher with a leadership challenge in 1990 suffered a major heart attack while on holiday in Venice in June 1993. Although he made a full recovery, delighting the Tory Party conference that year with his exercises on the platform, he had appeared very ill when he was flown back to Britain and had to spend months recuperating.
He bore a particularly stressful burden in the long election campaign and after Thursday's defeat and Mr Major's resignation many in the party were canvassing his name for "one last push" for the leadership.
He was seen as a compromise candidate who could reunite the party, bringing together Portillo supporters and pro-Europeans.
Sir Julian Critchley, former MP and friend since Oxford University days, said: "I think he had the potential to be a great prime minister, but in 1990 they decided he was too high-risk, he was dangerous, he was too ambitious... They invented John Major to keep him out."
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