Mihalis was born with Hypoplastic Right Heart Syndrome, a congenital condition in which the right-sided structures of the heart are underdeveloped or not formed.

When these structures are too small or do not function properly, the right side of the heart cannot send enough blood to the lungs.

The Marios family are sharing their story in the lead up to the HeartKids charity walk that will be held in Ballarat on Sunday to raise awareness and promote fundraising for the charity that has support them throughout their journey.

The family first made contact with the HeartKids after a 20 week pregnancy ultrasound revealed problems with Mihalis' heart.

The couple relocated to Melbourne 36 weeks into the pregnancy for Mihalis to be treated by specialists when he was born.

Mihalis had his first heart surgery at five-days-old and second surgery at three months. The family is now waiting for a date to be scheduled for his third surgery in the three step repair process to direct circulation of the blood.

While the surgery will be the final stage of circulation repair, mum Michelle Marios said Hypoplastic Right Heart Syndrome was a lifelong condition that needed constant monitoring and surgery intervention when required.

"For us as a family it is a daily struggle. It is keeping an eye on him and monitoring him through sight. If he ever has a fever he is taken straight to the emergency department," she said.

"Other than that it is day by day. We can't plan too far ahead because we don't know what is around the corner. It is our normal though, we don't know any different."

READ MORE: Toddler Mihalis Marios isn't letting the fact he has half a heart hold him back

Ms Marios said children with Mihali's condition have a life expectancy of about 30-years-old.

"With medicine always changing hopefully that is extended. But really they don't know," she said.

"The fact he is about to turn five is a huge milestone. Every day is a blessing."

Congenital heart disease is one of the leading causes of death of Australian babies under one and the most common birth abnormality affecting one in every 100 births.

There is no known cure. It is a complex chronic disease requiring lifelong treatment.

Ms Marios said support from HeartKids had been 'amazing' with a network of HeartKids families that have regular catch ups in Ballarat and support available when the family has been in Melbourne for surgery.

"The HeartKids families understand. You don't have to explain yourself. We are all going through it," she said.

READ MORE: Walking together for Ballarat's heart kids

HeartKids provides in-hospital and community-based support services that help families with financial and emotional support as they experience an emotional rollercoaster of hospital visits and ongoing treatments.

The HeartKids Two Feet and a Heartbeat charity walk in Ballarat on Sunday will raise funds and awareness for the organisation.

Participants can either walk 4km, in honour of the four Australian lives lost to congenital heart disease every week or 8km in recognition of the eight babies born with congenital heart disease every day.

The event commences with a special tribute ceremony that invites participants to lay flowers in memory of a Heart Angel that has been lost to congenital or acquired heart disease.

Anyone can register to participate online or on the event day at Victoria Park.

Visit heartkids.org.au/whats-on/two-feet-a-heartbeat-2019/locations for more information.