More than a thousand school children risk dropping dead from sudden heart failure, a grieving father has claimed.
They have cardiac abnormalities similar to that which struck down Armagh rugby player John McCall at just 18 years old, his said.
Ian McCall is pressing for screening of young people while they are in secondary school.
"John had a time bomb in his chest, we were totally unaware of that and on the afternoon of March 27, 2004, that time bomb exploded and we lost John," he said.
John was playing rugby for the Irish U-19 team in Durban, South Africa, when he died on the pitch. Ten days earlier he captained Royal School Armagh to victory in the final of the Ulster Schools Cup, the toughest match of his life.
Mr McCall said:" I can imagine John could be coming home at any stage; he left us to go to Durban and didn't come home."
He said one in every 250 children had undiagnosed abnormalities, equalling 1,330 pupils if pre-schooling was included.
"The unfortunate thing is that anything up to 80% of the cases don't present symptoms," he said.
The University of Ulster has already established facilities at Jordanstown which could be used if funding was provided to allow schools to undertake screening.
Other high-profile victims included former Tyrone GAA captain Cormac McAnallen (24), who was found dead in his Eglish home in 2004.
Today families' group Cardiac Risk in the Young (CRY) launched its postcard campaign. The postcard highlights the deaths of 12 young people from Northern Ireland of undiagnosed fatal heart conditions, most genetic.
Sport does not cause the problem but can exacerbate an existing, undiagnosed condition and young people are the high-risk group.
Conditions are treatable but in most cases the only way to discover who is at risk is screening.
OFMDFM junior ministers Jefferey Donaldson and Gerry Kelly attended the launch.
Mr Kelly said: "I understand that currently the Department of Health, Social Services and Public Safety is working with the other health departments, screening organisations and CRY to develop the evidence base on screening for sudden cardiac death."