Cardiologists have begun testing 600 children in the Far North to find those who may have suffered heart damage, as a result of rheumatic fever.
The disease is now rare in developed countries, but is still rife among Maori and Pacific Island communities in parts of New Zealand.
A team from Greenlane Hospital in Auckland is working with doctors and district nurses to screen children at Kaitaia between the ages of 10 - 13.
Similar testing on the East Coast and in South Auckland found up to 3% of children with damaged hearts, caused by undiagnosed episodes of rheumatic fever in childhood.
Northland Health says about two children per year at Kaitaia get rheumatic fever following a sore throat.
It says any children diagnosed by echocardiograms this week will be given monthly shots of penicillin until they reach adulthood, to ward off further bouts of the disease.
Northland Health says 130 people die every year in New Zealand as a result of subsequent heart valve damage.