Renowned heart specialist Professor Sir Magdi Yacoub today expressed delight at the successful outcome of a pioneering operation that restarted the original heart of a girl after her body rejected her donor organ.

Sir Magdi came out of retirement to advise on the groundbreaking surgery that reconnected 12-year-old Hannah Clark's own dormant heart - 10 years after he performed her heart transplant.

Hannah underwent the operation, believed to be the first of its kind in the UK, at London's Great Ormond Street hospital on February 20 after doctors discovered her body was rejecting her donor heart.

Sir Magdi was persuaded to come out of retirement to advise on the operation by Hannah's parents, Paul and Elizabeth Clark, of Mountain Ash in south Wales. The couple say their daughter is now recovering well.

The professor told BBC Breakfast that it was "not usual" for a transplant patient's original heart to be left in place, and that his surgical team had thought there was a chance Hannah's own heart would eventually recover.

"Her own heart has recovered. It really is absolutely wonderful news," he told the programme. "At the time we had the idea that she had this very severe muscle disease and there was the outside possibility that her heart would recover. That was the idea and it worked out, so that was wonderful. Now she is a happy little girl with her own normal heart. The complications have all gone. This is a very happy ending."

The transplant, carried out when Hannah was just two, saved her life because she had cardiomyopathy, which made her heart double the size it should have been and therefore likely to fail within a year. The donor heart worked fine until last November when a routine visit to a cardiologist revealed that her body was rejecting it.

Mrs Clark said surgeons at Great Ormond Street hospital were initially reluctant to remove her daughter's donor heart and reconnect the dormant one because they said it had never been done before. But the transplant team later agreed to perform the surgery.

Mrs Clark said: "Hannah recovered so well she was able to come home within five days. Nobody thought she would be like she is now. She is just enjoying her life and is looking forward to going back to Mountain Ash Comprehensive school after Easter. It has been like a breath of fresh air for her. She is doing a lot more by herself now and she is making me redundant!"

Professor Peter Weissberg, medical director of the British Heart Foundation, hailed the operation as an "exciting and important event".

He said: "Surgeons like BHF Professor Sir Magdi Yacoub have thought for some time that if a heart is failing because of acute inflammation, it might be able to recover if rested. This seems to be exactly what has happened in this case. The piggyback heart allowed the patient's own heart to take a rest.

"Today, the approach would be to implant a mechanical heart, called a ventricular assist device, to take over the work of the inflamed heart in the hope that the heart will recover and the device can be taken out after a few months. Ten years ago such devices were not sufficiently reliable, which is why Hannah received a donor heart alongside her own."

One major benefit of the operation is that Hannah no longer needs to take the strong anti-rejection drugs she was on while she had the donor heart.

She has also battled lymph cancer for the past few years but is currently in remission after a successful course of chemotherapy in January of this year.

A spokesman for the cardiac team at Great Street Ormond hospital said: "We are delighted that Hannah is doing so well. We believe that this combination of circumstances is the first for children or adults in the UK."