David Bennett had been in hospital for weeks. His heart condition was so bad that no conventional treatment would cure it. There was only one possibility left: an operation that had never been tried before. Doctors at the University of MarylandA state on the east coast of America. Its largest city is Baltimore. Medical Centre offered to give him a new heart, not from a human - but from a pig.

"He said to me two very important things," says Dr Bartley Griffith, one of the two leaders of the transplant team. "He said, 'I don't want to die,' and he said, 'If I do, maybe you'll learn something to help others.'"

The experimental operation took place on 7 January. Griffith and his colleague Muhammad M Mohiuddin had been working towards it for five years. But they had only been given permissionExperimental operations in the US have to be approved by the Food and Drug Administration, which is responsible for protecting public health. to try it a week earlier. 

Before the operation, there were several ethical concerns to be addressed. Since it was so risky, Bennett was interviewed four times by psychiatrists to make sure he realised what he was agreeing to. Everyone in the medical team was told that they need not take part if they felt worried about it. 

Bennett was also a controversial choice of patient. He had a record of failing to take his prescribed medication and had spent several years in prison for stabbing a man. But the hospital insisted that it was his medical needs, not his character, that mattered.

The main danger with a transplant is that the body will recognise the new organ as something that does not belong to it, and the immune system will fight against it. To try to stop this, drugs called immunosuppressants have been developed. Unfortunately, they also lower the body's resistance to infections.

On the morning of the operation, Dr Mohiuddin collected a heart that had been removed from a genetically modified pig and placed in a special containerIt keeps the heart cold and pumps fluid through it. to keep it alive. Ten of the animal's 30,000 genes had been alteredThey included a gene that controls how large and fast the heart grows. to reduce the chances of a human rejecting it.

The operation was an extraordinary successSuccess is when you reach your aim or purpose. . When the new heart was connected to Bennett's blood vessels, says Dr Griffith, "It was as if we'd turned on a light. And it was a red light. The heart just brightened up. And it went from trembling to pumping."

By the end of the day, Bennett was strong enough to thank his doctors. "That was a huge sigh of relief and peace to everyone," his son remembers.

At present, there are many more people needing a transplant than there are organs available to give them. In the US, there are over 100,000 patients on the waiting listThe list is the longest for people needing kidney transplants., with another added every nine minutes.

As a result, governments are asking everyone to donate their organs to others. The organs from one person's body can save the livesThey can also improve the lives of 75 others. of eight others.

But not everyone is happy to go along with this - so a transplant from a pig could be a hugely important alternative.

Yes:  There is very little difference between being given a heart from a pig and one from another human being. And if the operation is a life-saving one, then no recipient can afford to be fussy.

No: The idea is completely unnatural. With a human heart, the donor has at least given their consent. It would be unbearable to think that a pig had been bred and killed in order to prolong your life.   

Or... This should be a reciprocal arrangement. There must be things that we can do to prolong animals' lives - including donating our organs to them - so scientists should be working on that too.

UPDATE: David Bennett died on 9 March 2022. Senior doctors hailed him as a "brave man" who had helped to advance medical science by taking part in the surgery. The core debate around this story remains the same considering the amount of time Bennett survived and his contribution to the future of transplant medicine.