Cardiac arrests are one of the biggest killers of Australians under 50, and doctors say more research is needed

There were few signs Bryan Maris was unwell before he died in his sleep at the age of 31.

“I climbed in [to bed] beside Bryan and I lay beside him and he wasn’t responding, and that’s when I realised that something wasn’t OK,” his wife Jessica Maris said.

Despite her and ambulance workers’ efforts to revive him, Mr Maris died.

And six years on from his death, his family still does not know what caused it.

“He was completely healthy,” Mrs Maris said.

“He raced A-Grade cycling, he was super fit, super athletic, just…