By Jane Elliott
BBC News health reporter
As a baby Stephen Proffitt had difficulty feeding and failed to thrive.
Stephen was discharged the day after his op
When he was just three months old, his parents faced their worst nightmare as they were told their baby had a major heart defect and would need urgent open-heart surgery.
He was born with a condition called truncus arterosis, which means he had only one large artery instead of the usual two - pulmonary artery and aorta.
The operation to insert a donor pulmonary artery and to patch a hole between the pumping chambers was a success and Stephen spent 10 days recovering in hospital.
But shortly before his second birthday, tests showed that the conduit that had been inserted had narrowed and further surgery was needed to replace it.
Once again Stephen had open-heart surgery.
And because he was still growing, surgeons anticipated that he would need further surgery every few years.
Last December, Stephen and his family noticed that again he was becoming more breathless and tired and less able to keep up with his friends in football.
Surgeons said he would need a third procedure, but this time he was selected for a new technique, performed at Great Ormond Street by Professor Phillip Bonhoeffer, which would mean there was no need to open his chest.
The one-hour procedure, first used five years ago, uses a catheter (long thin tube) inserted through the leg to guide a valve gently through the heart and into the pulmonary artery.
Stephen, now aged 10, had the procedure and his father said they had all been happy with it, particularly as it has a much lower risk than traditional open-heart surgery.
He said Stephen's recovery had been dramatic.
"He had the operation last December on a Tuesday and he had left hospital by the next day.
"We went up to the hospital on the train and after the operation he was in a good enough condition to walk back to the train.
"He even went to a school play on the Thursday and was ready for football training on the Saturday.
"Before his illness, he was not able to keep up with the others on the football pitch but he enjoyed his game.
"He was about a pitch behind them in training in the five-a-side, but within two weeks of the operation he was just half a pitch behind them. It was a big improvement."
Mr Proffitt said it was not known whether Stephen would need further surgery, or of what type.
"They are very pleased with his progress.
"They have said they can't rule out that he will have to have open-heart surgery. But that this operation will buy us more time."
The Great Ormond Street team have carried out 100 such procedures, and on Monday a group of young patients will gather in London to celebrate.
Professor Bonhoeffer, consultant paediatric cardiologist at Great Ormond Street, is now helping others to acquire the technique and hopes it will soon be rolled out world-wide.
He said he first established the technique after being concerned when open-heart surgery had left one of his patients feeling worse than before and although he had done everything possible he was sure there was a better way of carrying it out.
In 1999, he began a pioneering research programme with the aim of replacing a pulmonary heart valve without open-heart surgery.
He performed the world's first human heart valve implantation without surgery on a 12 year-old boy in France in September 2000, before joining Great Ormond Street Hospital in 2001.
"Initially I thought that the realisation of the idea was impossible because it seemed too easy.
"But, having found the right valve, I was amazed to see the concept work.
Professor Bonhoeffer stressed that, because the procedures were so new, he always made sure the families, particularly of the first patient, were fully aware of this.
"I told my first family that I did not know what the risk was. We thought the risk was probably not high and over the 100 operations we have done we have not had any deaths or any long-lasting consequences.
"But I always had a close relationship with the families involved, because I wanted them to know what I was doing so they could truly understand the unknown."
But he said all the operations had gone smoothly.
Talking about the first operation he said: "When we implanted the valve it was beautiful to see how immediately the patients improved, they were not in pain and did not require intensive care.
"This much less-invasive procedure also avoided the need for open-heart surgery and enabled patients to leave hospital within a day of undergoing the procedure."
And he said that each time they carried it out they learnt from previous time and each time it became easier.
"Having completed over 100 cases I am now very much looking forward to seeing the technique being rolled out worldwide."
Dr Charmaine Griffiths, spokesperson at the British Heart Foundation (BHF), said: "We're delighted to have funded Professor Bonhoeffer's work, which is a real advance in replacing heart valves without the need for major surgery.
"This is hugely important for children as they don't have to go through a traumatic operation and suffer from the physical and emotional scars that go with open heart surgery.
"Professor Bonhoeffer's work has paved the way for similar approaches to valve replacement in adults who may be too sick or frail to undergo a major operation."