By Fergus Walsh
Medical correspondent, BBC News
Routine heart transplants have been suspended at Cambridgeshire's world famous Papworth Hospital after a rise in the early deaths of patients.
There is a growing shortage of donor hearts
This year seven of the 20 adult heart transplant patients have died within 30 days of their operation.
The hospital says the UK average death rate is 10% and its normal rate is 7%.
Papworth has remained at the forefront of heart transplant surgery ever since it carried out the UK's first successful operation in 1979.
But it is a sad reality that some patients do not survive transplantation.
The question is why the mortality rate at Papworth should have leaped from 7% to 35%.
Persistent technical error by the transplant team is possible but thought to be unlikely.
Four surgeons are involved in removing and transplanting the organ and problems should emerge quickly.
Fewer and fewer hearts are becoming available so the quality of donor organs may be an issue.
In 1996 276 heart transplants were carried out but in 2006 this had fallen to 156.
Improved techniques mean surgeons can use hearts which previously would have been rejected.
The likeliest problem may be the poor health of the recipients.
Patients are now spending longer on waiting lists which means they are getting sicker.
Heart support machines can now keep patients alive who previously would have died before being considered for a new heart.
The facilities at Papworth may also be a factor.
On its website Papworth says "these services are currently provided on a cramped site of buildings, many of which were not designed for the delivery of modern healthcare, and this is threatening to compromise the high standards and patient outcomes for which the hospital is renowned."
Professor Peter Weissberg, medical director of the British Heart Foundation, stressed that no matter how skilled the surgical team, things could go wrong.
He said: "Despite the huge advances that have been made, heart transplantation is
still a high-risk procedure carried out on extremely ill patients."