But now little battler Kerr McGrath is about to turn five - and is heading off for his first day of school.
Kerr was born with a rare heart defect, double inlet/double outlet right ventricle, a condition that affects just five in 100,000 people.
When he was just days old his mum, Margaret O'Malley, and dad, James McGrath, were given the option to let him slip away.
But the couple wanted to give their boy a fighting chance and now he's confounding expectations by starting P1 at St Paul's Primary, in Shettleston.
And his first day comes just five weeks after he had an eight-hour open heart operation.
Margaret said: "We're so proud of Kerr as he starts school.
"It's a day we thought we might not see so it's so wonderful how well he's done.
"We've spoken to the school to explain that Kerr needs extra care and they have been great about it. He's looking forward to his first day."
Although Margaret had a healthy pregnancy, Kerr was born one month early and was taken straight into the neonatal unit at the Princess Royal Maternity Hospital.
Doctors suspected all was not well with the infant and a heart scan confirmed their fears.
At three days old Kerr was rushed to Yorkhill Sick Kids' Hospital to see a heart specialist.
Margaret, 35, said: "My previous two pregnancies were small babies so I was scanned regularly throughout my pregnancy with Kerr and everything seemed fine until he was born one month early.
"Doctors said he was missing a chamber in his heart, it came out of the blue, there was no history of heart problems in the family, this was something we had never heard of.
"It was just a big, big shock - we didn't even know babies could have heart problems like this.
"The most difficult thing, really, was the shock, as there was no sign of it during my pregnancy. Sometimes it is diagnosed while the baby is in the womb so, even though it's still terrible, at least those parents have the chance to come to terms with it and find out more information."
While Margaret and James, who are also mum and dad to Kian, 10; Riley, seven; and Reede, 15 months, were still struggling to come to terms with what was happening to their new baby, they were faced with a terrible choice.
Margaret added: "He was in intensive care and the consultant thought there was nothing they could do as he couldn't live without the part they thought was he was missing.
"They gave us the choice to let him go, but we wanted to let him fight."
Kerr's first operation lasted six hours - though Margaret said it felt much longer - and he was finally allowed home one month later.
Since then, the family have had to cope with dozens of hospital visits and two further eight-hour open heart operations.
The second of these was on July 8 - just weeks before the start of school.
Margaret said they would not have coped without the support of family and friends, who babysit while Margaret and James, 36, are at Yorkhill.
Big brother Kian frets over his little brother but will be there to support him at school.
Margaret said: "We try to be as honest as possible with Kian and Riley without terrifying them.
"Riley has never known life without Kerr, but Kian finds it very hard and worries a lot, especially when Kerr is in hospital. He's a great big brother."
It is possible that Kerr will still need further surgery as he grows and the family are very careful with his health.
He tires easily and takes the blood thinner warfarin, which means he also needs to watch out for cuts or bumps.
But Kerr, who turns five next month, is delighted to be off to school and his mum and dad couldn't be any prouder.
Margaret added: "Hopefully he doesn't need anything else after having these three operations but you never know what's around the corner.
"They basically changed the circulation in his body to go in a different direction and this last surgery is hoped will give him a better quality of life.
"His oxygen levels are very low and so he has very little energy but we have noticed a bit of a change since this surgery.
"He's going to be great at school and we're so proud of him. It's a milestone for him and for the family."