Hannah Clark is a transplant patient with a difference: when she was two years old, she had to have an extra heart grafted on to her own. Jerome Taylor hears her story

For 10 years, Hannah Clark was known as the girl with two hearts. She was barely a year old when her parents rushed her to hospital because the tiny heart she had been born with simply wasn't strong enough to pump blood around her body.

Faced with certain death, doctors were forced to perform a life-saving transplant when she was aged two. But instead of removing the sick heart altogether, they grafted a donor heart on to her own one, allowing the weaker organ to rest and rebuild inside her body. Life became a constant struggle as Hannah's immune system slowly began to reject her transplant.

But yesterday, in her first public appearance, the healthy 16-year-old from Mountain Ash, South Wales, spoke of her delight at being given her original heart back after becoming the first person in Britain to have an organ transplant reversed.

"It was really strange, I felt empty," Hannah said of the moment she awoke after the groundbreaking operation and realised her real heart was pumping fully for the first time in a decade.

"A second heart had been inside of me for so long but all of a sudden it was gone. I could actually feel that something was missing in my chest. But I was so happy."

The surgery to give Hannah use of her original heart again took place at Great Ormond Street Hospital in February 2006. Yesterday, the specialists behind her groundbreaking operation were reunited with the teenager to mark the publication of the team's findings in the Lancet journal.

Sir Magdi Yacoub, a transplant pioneer and the doctor involved in Hannah's original transplant 15 years ago, described the operation as "unique" and said her recovery proved how it was possible to restore a once-weak heart that had been allowed to recover inside the body using support from a healthy donor organ.

Sir Magdi, who came out of retirement to help with the reversal of Hannah's original transplant, said: "The possibility of recovery of the heart is just like magic. A heart which was not contracting at all at the time we put in a new heart now functions normally."

Until the transplant was reversed, Hannah's life had revolved around a constant routine of medication to keep her immune system suppressed and regular visits to the hospital.

Born with cardiomyopathy, a heart disease which occurs in about 1.2 children for every 100,000, Hannah was given months to live, until a donor heart was found. But, afraid that her body might reject the transplanted organ, doctors inserted the new heart alongside her weak one which, once allowed to rest, began to recover.

Although her new heart saved her life, it also left the exercise-mad teenager, whose favourite hobbies are now swimming and shopping, painfully vulnerable to infections and malignant growths which are often caused by a suppressed immune system.

She had to undergo two sessions of chemotherapy and at one point was put on a ventilator because a cancerous growth was crushing her windpipe. By November 2005, when she was aged 12, a scan showed that Hannah's body was beginning to reject her transplant and doctors decided that they had no alternative but to take out the transplanted heart and hope that her old heart had become strong enough to operate independently.

Five days after the transplant was reversed, Hannah was back at home and no longer having to take a cocktail of 17 drugs each morning. She has a summer job working with animals – something that would have been unthinkable on a suppressed immune system – and returns to sixth form college in September to study child care. "I would like to work with animals or children or in a hospital," she said.

Fighting back tears, Hannah's parents, Paul and Liz, described how the operation and given them their daughter back. "Our life has been changed from a normal life to upside down and now we've got it back again," said Mr Clark, a 45-year-old lorry driver.

"Hannah's life before the operation, when she was 10 months old, was very traumatic. She was going from one extreme to the other. She needed a donor heart so badly, it was just like a rollercoaster ride.

"It was very worrying and stressful but we just kept on and made her fight for it. We would tell her 'Come on Hannah, you can't give up, you've got to keep going'. And here she is today."

The only way they coped, the couple said, was to never give up hope that their daughter would pull through. Mr Clark recalled one moment when his daughter had been rushed to hospital suffering from seizures as a result of a series of cancerous growths pushing down on her spinal chord. "This nurse came in and told us that our daughter had just 12 hours to live. I just said 'You believe what you want to and I'll believe what I believe, which is that she will pull through'."

Both parents have called on the Government to change the rules governing organ donorship to "presumed consent" where people would have to opt out of being a donor rather than opt in, under the current guidelines. Experts at the British Medical Association and the Royal College of Surgeons say an opt-out clause could save hundreds of lives a year and stop agonising waits for those on the donor list.

"Until it happens to you, you don't realise how important it is to be a donor," Mr Clark said. "People often say 'I need [my organs]'. Well you don't. Somebody else needs them. People don't realise until it happens to them how it can change your life."

His wife said: "I would just like to say a big thank you to the donor because they lost a child but we gained a child. I could have lost my daughter but they gave me my daughter back."