Six months after his quadruple heart bypass, Bill Clinton will be back in hospital in New York tomorrow for surgery to remove scar tissue and excess fluid from his left chest.

Six months after his quadruple heart bypass, Bill Clinton will be back in hospital in New York tomorrow for surgery to remove scar tissue and excess fluid from his chest.

The news, which caught doctors and close associates of the former president by surprise, came a few hours before Mr Clinton and President George Bush's father were due to appear at a White House event to report on tsunami relief efforts in south Asia. Both former presidents have just returned from a trip to the region.

Mr Clinton's condition, where the lining of the heart becomes inflamed and fluid builds up around it, is a relatively rare consequence of heart surgery.

But it is not considered especially serious, unless it is left untreated for a long time. The former president seemed to be in good form yesterday, waving and joking to reporters as he left a meeting at the State Department.

His doctors said that they expected "a full functional recovery". Mr Clinton is likely to remain at the Columbia University Medical Centre for between three and 10 days.

According to a statement from his office, the fluid build-up, which had spread to the left lung, had caused Mr Clinton "some discomfort" in recent weeks, but that otherwise the former president ­ now noticeably slimmer than in his White House days ­ was in good condition.

Since emerging from the original surgery on 6 September last year, he has maintained a busy schedule ­ if anything too busy, some associates suggested. Mr Clinton went out on the campaign trail for the Democratic nominee John Kerry, and then presided over the opening of his presidential library in Little Rock, Arkansas.

This year, along with the former President Bush, he has helped co-ordinate private sector tsunami relief in the US.

"I would just like Senator [Hillary Rodham] Clinton to make sure he takes it easy for a while," joked Dianne Feinstein, Mrs Clinton's Democratic colleague from California.