The right hand man of top racehorse trainer John Quinn was a victim of Sudden Adult Death Syndrome when he died in his sleep, an inquest heard.
Sean McGuinness, 24, had been battling a hole in the heart condition which ended his promising racing career in Ireland, it was said.
Girlfriend Charlotte Buckle told last week’s hearing at Scarborough that Sean went to bed at 10.30pm at their home in Norton and never woke up.
“Sean did not get up which was unusual because he loved his job and would normally bound out of bed to go,” she said.
She touched his face and it was cold, so she slapped him and when he still failed to respond she started CPR until the ambulance arrived.
A specialist examination by Prof Mary Stephenson in London showed Mr McGuinness had died from heart failure due to an irregularity in the beating of the heart.
There was no tissue damage and the heart was not an unusual size. Prof Stephenson agreed with other experts that death was due to Sudden Adult Death Syndrome, an unusual but well recorded condition.
As a jockey, Sean had rode three or four winners in Ireland. But the hearing was told he was ordered to give up his career by the sport’s medical board after being diagnosed with a hole in the heart.
He had been appointed assistant racecourse trainer at Mr Quinn’s yard in Malton less than a year before the tragedy in January.
Recording a verdict of natural causes, North Yorkshire East Coroner Michael Oakley said it was clear the heart appeared normal.
But it was also apparent he had suffered from an arrhythmia or some other condition which affected the operation of the heart but would not show up after death.
The hearing at Scarboroug Rugby club was told Sean’s family would have be tested for the condition but his parents in Ireland had already been given a clean bill of health.