Thirty years ago this month Dr Christiaan Barnard performed the first successful human heart transplant in Cape Town in South Africa. He pioneered a kind of medical miracle that is now almost routine. It is just one of a number of organ transplants carried out every day to save lives.

This week it was revealed that baby Baebhan Schuttke from Dublin had become the youngest recipient of a transplanted organ when she was just five days old. When the baby was born in July, she developed liver failure. Baebhan was transferred to King's College Hospital in London and, using a new technique in liver transplantation, surgeons replaced her liver with a section of a liver from a 10-year-old boy who had died in an accident. They had discovered that each of the liver's eight segments can work independently.

The advantage of carrying out surgery on such a young baby is that the body is so new, the immune system does not reject the organ as alien. It is hoped that in time Baebhan may even be able to stop taking the immuno-suppressant drugs which prevent the body from rejecting the liver.

Transplantation of hearts, livers, kidneys, pancreas, lungs and corneas is commonplace, but further developments in transplant surgery are controversial. Possibilities include implanting patients with the bone marrow of a baboon or the heart of a pig. This is xenotransplantation, adapting animal organs for humans.

Elsewhere artificial hearts are being further refined, and the possibility of banishing blindness through inserting a microchip in the eye is being investigated. However, according to Michael O'Keeffe, ophthalmic surgeon at the Mater Hospital, there is no question at present of a whole eye being transplanted. "It is just not possible," he said.

Research into xenotransplantation is good news for people waiting for transplants, particularly in the US where more than 50,000 patients are awaiting organs, but with fewer than 5,000 human donors annually. It involves the use of live, non-human animal cells, tissues and organs in human patients. Pigs are good potential donors because their organs are about the same size as human organs and work similarly. There is also a lot known about raising pigs and they are readily available.

"A lot of effort has gone into the pig," said Patrick Cunningham, Professor of Animal Genetics in Trinity College. "They are trying to produce animals that have organs that could be transplants into humans. It involves transferring human genes into pigs so that the organs produced are more human." Liver xenotrans plantation is also being investigated.

This use of animal organs and tissue in humans could provide a lifeline, either as a bridge to human organ transplant, or as a long-term solution to the organ shortage. However, it raises many novel medical, legal and ethical issues.

Medical concerns centre partly on organ rejection, but include the possible risk of infection. Organisms in host animals may be transferable to humans. These may have long incubation periods in humans, necessitating long-term monitoring of the transplant patient.

The animals used for transplantation would need close monitoring and screening for pathogens. But xenotransplanters point out that in the handful of transplants that have already happened none of the patients has died from an unknown disease. Equally, though, no patient has lived for long enough after the operation to make doctors confident that they were disease-free. "Concern is increasing about this," said Prof Cunningham. "There is a big fear about the transfer of viruses. They may be harmless in animals but could turn nasty in humans, remembering that AIDS came from monkeys."

High hopes were held out for the artificial heart but faded quickly because of infection and stroke. These hearts are also very expensive, costing around £70,000. They are now being used as an interim measure while a patient is awaiting transplant to keep them alive. "There are huge financial implications and you have to have someone watching the patients all the time," explained cardio-thoracic surgeon Mr Maurice Neligan, who performs heart transplants at the Mater Hospital.

Intensive research is ongoing in this area. In the US scientists and experts in rotating equipment and magnetic bearings are collaborating on the next generation of artificial heart pumps.

With regard to liver transplants, Mr Aidan McCormick, consultant hepatologist at St Vincent's Hospital, said splitting the liver is an important development in countries, unlike Ireland, where they have major organ shortages. Living donor transplants have been carried out where a part of a parent's liver has been taken for a child. "About 500 such procedures have been carried out worldwide and there has been just one donor morality," said Mr McCormick.

Kidneys were the pioneering organs in transplantation in the 1950s, according to Mr David Hickey, transplant surgeon at Beaumont Hospital. Transplantation of the pancreas is relatively new. It is carried out on a small percentage of the large population of diabetics, who have difficulties producing insulin.

A variation on this is an islet transplant. "The islets produce the insulin in the pancreas," said Dr Hickey. "However, you need a number of donors for this procedure, which is a waste of organs at the moment. It will become important in the future for a number of diabetics. Putting the islets into a chamber and implanting them in the skin with the blood supply running past has been tried in dogs and is very promising."

Although it is essential for life, when a person needs an organ transplant the immune system suddenly becomes a deadly force, attacking and destroying the implant. But immune-system-suppressing drugs such as cyclosporine have made organ transplantation possible by restricting attack on the transplanted organ while sparing the immune system's most life-saving benefits.

Prof Michael Ryan, Professor of Pharmacology in UCD, said that immuno-suppressants revolutionised organ transplantation in the past 10 years. However, one of the major side-effects has been kidney damage. Medical research into transplant technology and biology is an exciting field, with much work being done to try and solve the problem of organ rejection. As yet there is no human survivor with a functioning animal's organ, but it appears to be only a matter of time.