When Helen Clarey gave birth a year ago, she was told it was unlikely her son, Noah, would survive because his heart was the size of a thumbnail.
But yesterday, Mrs Clarey, her husband Neil and their daughter Phoebe, five, gathered to celebrate Noah's first birthday.
Mrs Clarey told Chronicle Live: "We feel so lucky to have him here on this special day."
Mrs Clarey's waters unexpectedly broke when she was 22 weeks pregnant and she was warned she would go into labour within 48 hours.
"They also said I should prepare myself for the fact that there was no chance the baby would survive," said Clarey.
However, doctors managed to delay her labour for four weeks and Noah was born on 28 May 2014.
Noah weighed only 2lbs 2oz when he was born and was taken away to the special care unit.
Unsure whether or not their newborn son would survive, Clarey and her husband, Neil Clarey told the Durham Times: "It was a roller-coaster experience. When he came out he looked like a jelly baby and sounded like a little kitten."
Noah managed to cope well during his first couple of weeks, but when he was five weeks old his parents found out a duct in his heart was wide open and needed to be closed immediately in a 30-minute operation.
Noah, who at this point weighed just 3lb, was transferred to a different hospital to close the hole.
Doctors told Mrs Clarey that her son's heart was the size of a thumbnail when they performed complex heart surgery to save his life.
After the operation, he gradually started showing signs of recovery and was described by his parents as being a "true fighter".
Noah is now showing no signs of the problems he faced when only a couple of months old.
His parents say they could not have made it through the past year without the help of the Tiny Lives Trust charity at the RVI hospital in Newcastle upon Tyne.
Mrs Clarey told Chronicle Live: "Without the help of Tiny Lives Trust, babies in special care would not do as well."