Jamie Parkhouse often found himself short of breath after playing football but the plucky 13-year-old had always put it down to asthma.
That was until last month, when the youngster suffered two heart attacks at his home in Southall and medics discovered he had a hole in his heart.
Football and other forms of vigorous exercise are now strictly off the cards, but that hasn't stopped Jamie attending Heston Cadets every week.
The Heston Community School pupil was even chosen by the 192 Heston Detachment of the Army Cadet Force to join the guard of honour at this year's Remembrance service.
"I have to pace myself but I love coming here and everyone's always looking out for me," he said.
"I've made lots of friends and all the activities here, especially the camps, really help take my mind off things."
Jamie's determination typifies the spirit of the 40-odd cadets, aged 12-18, who meet every Monday and Wednesday night at the centre in Vicarage Farm Road, Heston.
Many worried parents view the cadets as little more than a recruitment camp for the Army, but members point out that couldn't be further from the truth.
"Youngsters complain there's nothing to do, so they join gangs and walk round the park in hoodies, but there's plenty out there if you're willing to give it a go," said Sergeant Brijinder Nijjar, 17, who joined with his brother Harmeet, 16, four years ago.
"You get opportunities to do things you could never afford otherwise, like diving and skiing, and a weekend away costs just £10."
Youngsters handle the same weapons used by soldiers in Iraq and Afghanistan, with minor safety adjustments.
But instructor Staff Sgt Priscilla Ledlie insisted the training made them more aware of the dangers of carrying guns and knives.
"We're teaching youngsters to be safe with weapons, to appreciate their capabilities and realise they're not just tools for killing," she said.
The cadets is about much more than shining your boots, with members organising charity events and picking up skills that help with everything from applying to university to finding a job.
And, far from glamourising war, Harmeet said his time with the cadets had given him a new-found respect for the sacrifices made by soldiers in Iraq and Afghanistan.
"When you're on a training camp and you can see who's shooting at you, you think if that was a live round I could be dead," he added.
Fellow cadet Mitchell Dye's dad Alan spent two years in the Army Air Corps before his son was born, which fuelled Mitchell's desire to join the cadets.
"I wanted to know what it was like for my dad and I've really enjoyed it so far," said the 12-year-old, of Worthing Road, Heston.
"My favourite bit's the virtual shooting range, which is just like the real thing except you use a laser-guided gun with compressed air to give an authentic recoil."
Another enthusiastic recruit is 13-year-old Amal Metla of Blossom Way, Heston.
His 15-year-old sister Jyoti is also an army cadet, while his eldest sister Kirandeep, 21, is an instructor with the air cadets.
"Kirandeep's always trying to get me to join the air cadets but I like it here," said the Lampton School pupil.
"I love the camps and inter-service competitions and It's really made me think about joining the Army."