Charity campaigner Vera Looker manned a stall in the Cascades shopping centre to try to raise awareness of a condition that kills four to eight children a week in the UK.
Mrs Looker, 60, of The Dale In Widley, lost her 21-year-old son Michael to an undiagnosed heart condition 16 years ago. She says that at the time not much was known about such conditions, which result in sudden death syndrome (SDS) and there was little help for bereaved relatives.
Ten years ago, national charity Cardiac Risk in the Young (CRY), was set up and Mrs Looker and her husband, Geoff, joined the team to try to raise more awareness of the undetected heart conditions that are killing apparently fit and healthy young people.
Mrs Looker, Hampshire rep for CRY, said: "A post-mortem showed that Michael had an undetected heart condition which had resulted in SDS. Two other young people in our extended family have also died of SDS.
"I have five grandchildren and for their sake I would like to see some sort of screening in place."
CRY is now in its tenth year and provides medical information on the most common causes of unexpected cardiac death in people aged under 35.
The majority of sudden deaths are caused by inherited forms of heart muscle disorder and an irregular heartbeat. Abnormalities can be diagnosed by an electrocardiograph test and can then be treated. CRY wants screening by GPs to try to prevent sudden deaths.
It also raises awareness of cardiac abnormalities in young people and offers support and counselling.