The girls with 2 hearts..

LONDON, England (CNN) -- Hannah Clark is a 16-year-old with a shy laugh and a love of animals. She likes to go shopping with friends and dreams of a career working with children.

But Hannah Clark is no ordinary teenager and her normal life today could not have been possible without a unique, life-changing heart surgery.

In 1994 when she was eight-months-old, Hannah was diagnosed with cardiomyopathy -- an inflammation of the heart muscle that impairs the heart's ability to work properly.

Hannah's heart was failing and she needed a transplant. But instead of taking her own heart out, doctors added a new donated heart to her own when she was just two-years-old.

The so-called "piggyback" operation allowed the donor heart to do the work while Hannah's heart rested.

But Hannah was not in the clear yet. As with any organ transplant, Hannah's body was likely to reject her new heart and she had to take powerful immune suppression drugs.

Those drugs allowed her body to accept the donor heart but also led to lung cancer (nice side effect) and yet another medical battle for Hannah that lasted for years.

Nearly 11 years after receiving the extra heart, there was more bad news: The immuno-suppression drugs were no longer working. Hannah's body was rejecting the donor heart.

In February 2006, her doctors tried something that had never been done before: They took out the donor heart. Doctors theorized that the donor heart had allowed Hannah's heart to rest, recover and grow back stronger.

Now for the first time Hannah's father, Paul Clark, describes the agonizing decision the family had to make at the time: "If she'd never had it done, she wouldn't be here.

"In the very beginning it was a 50/50 chance she wasn't going to make the operation. But in the next one it was even greater because it had never been done before. But we had to take that risk," he told CNN.

The doctors were right. Three years later, Hannah has no need for any drugs and has been given a clean bill of health. The operation was a success.

"It means everything to me," Hannah told CNN after the pioneering operation. "I thought I'd still have problems when I had this operation done. I thought after the heart had been removed I thought I'd have to visit hospitals. But now I'm just free," she said, smiling.

Dr. Magdi Yacoub performed Hannah's original transplant and came out of retirement to perform the second.

"The possibility of recovery of the heart is just like magic." Dr. Yacoub said at a media conference. "[We had] a heart which was not contracting at all at the time. We put the new heart to be pumping next to it and take its work, now [it] is functioning normally."

The findings have been published in the British medical journal, the Lancet.

Hannah's amazing recovery would not have been possible without a donor. Both Hannah's doctors and her family made an appeal for more people to consider organ donation.

"When it happens to someone close to you or yourself, you don't realize until then how important it is to be a donor and not to be selfish like, I need that part. You don't need that part. Give it to somebody else that needs it," said Clark.

"It just proves that if you can, be a donor. This can happen."

Dr. Yacoub now advocates "presumed consent" -- a policy by which anyone can be considered an organ donor unless they specifically request to opt out.

"All you are asking is please make up your own mind. Do you or do you not want to be a donor? My own family, my kids, everybody wants to be a donor. But if you don't, then say so," he said.

"Just please tell us what you want to do. So, presumed consent is a good thing."

Hannah has made a full recovery and looks forward to doing what many teenagers do during the summer holidays: Work at a summer job. Her family jokes that it's difficult to keep her from racing out the door now that she has so much energy.

For Hannah, it took the strength of two to help heal a broken heart, something she could have never done alone (wow, cheesy writing).