Runners and walkers are clocking up the kilometres, and more importantly dollars, on the treadmill today as part of a 12 hour treadmill challenge for Heart Kids NZ.

From 7am to 7pm today, Jetts 24 Hour Fitness branches in Tauranga and Bethlehem are taking on the Treadathon Challenge in support of children affected by congenital heart disease.

Heart Kids BOP committee member Alicia Gestro prepares to take over from Jetts 24 Hour Fitness manager Darryl Gove, Ethan Jeffs and Josh Svendsen. Photo: Bruce Barnard.

Split into 22 half hour time slots, the challenge sees each runner donate $5 to get on the treadmill, where they walk or run for 30 minutes before swapping.

Heart Kids is the only New Zealand charity supporting Kiwi children and their families affected by congenital heart disease.

Heart Kids receives no government funding, and with 12 babies born in NZ each week with the condition, they need help to keep providing children with support when they need it most.

Tauranga's Jetts 24 Hour Fitness manager Darryl Gove says it is a great cause to get behind.

They were so keen to help out, gym members started running an hour early.

Already lined up to take part are ANZ members from the Elizabeth Street branch who are giving up half an hour throughout the day to come down and run.

Having already clocked up his 30 minutes this morning, Darryl says there is the possibility he might be required to jump back on as there are a handful of time slots still unallocated.

So far the inaugural event has raised more than $12,000.

Heart Kids BOP committee member Alicia Gestro says it is great to see Jetts get behind Heart Kids NZ and raise vital funds.

The cause is extra special for Alicia as two of her four children are born with heart defects, 13-year-old Thomas and four-year-old Quin.

Talking to SunLive while on the treadmill, Alicia says in the Bay of Plenty there are about 120 families registered with Heart Kids – ranging from babies through to adults.

'Once a heart kid always a heart kid. You don't outgrow it, you don't fix it.

'It's a good way to get your exercise in and raise money and awareness at the same time.”

The funds raised will help Heart Kids support the 600 new heart families who will welcome a heart baby to their lives this year alone.

It will help provide emotional and practical support for parents as they sit by their child's bedside following open heart surgery on their little one.

It will help send heart kids from all across the country to camps, where they can experience what their peers sometimes take for granted, in a safe and confidence-building environment where they'll make life-long friends with other kids who really 'get' what they're going through.

The impact of CHD is far-reaching. It is the most common birth abnormality and the main cause of infant and children mortality in New Zealand, and yet there is neither prevention nor cure.