David Bennett's heart condition was so bad that no conventional treatment would cure it. There was only one possibility: an operation that had never been tried. 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 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 operation took place on 7 January. Griffith and his colleague Muhammad M Mohiuddin had been working towards it for five years. 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. 

There were several ethical concerns to be addressed. Bennett was interviewed four times by psychiatrists to make sure he realised what he was agreeing to. Everyone in the medical team was told they need not take part if they felt worried. 

Bennett also had a record of failing to take his prescribed medication and had spent several years in prison for stabbing a man. The hospital insisted 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. To try to stop this, drugs called immunosuppressants have been developed. 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 a successSuccess is when you reach your aim or purpose. .

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.

There are many more people needing a transplant than there are organs available. 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. The organs from one person's body can save the livesThey can also improve the lives of 75 others. of eight others.

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.

Maryland - A state on the east coast of America. Its largest city is Baltimore.

Given permission - Experimental operations in the US have to be approved by the Food and Drug Administration, which is responsible for protecting public health.

Special container - It keeps the heart cold and pumps fluid through it.

Altered - They included a gene that controls how large and fast the heart grows.

Success - Everything has gone well so far, but the team will continue to monitor Bennett for several months.

Waiting list - The list is the longest for people needing kidney transplants.

Save the lives - They can also improve the lives of 75 others.