A man died suddenly at home with his partner by his side.
Andrew Marsh, 52, woke his partner in the middle of the night complaining about chest pain.
Tommy Milne who lived with Andrew in Grangetown, said they went to bed at around 9.30pm and nothing seemed wrong.
He said Andrew worked as front of house manager at St David's Hall in Cardiff and had recently been working for Test Trace Protect within Cardiff and the Vale University Health Board.
Tommy, 24, said: "He woke me up in the middle of the night complaining of chest pain and I called the ambulance immediately. He had a fit on the bed while the ambulance was on the way.
"His breathing became really slow. I rang the ambulance back and they gave me advice on how to do CPR."
When paramedics arrived he watched in desperation as they tried to save Mr Marsh.
"They came and told me it isn't looking good and that they couldn't do anything else," he said.
"I lay next to him until his body was taken away."
Andrew suffered a heart attack two years ago but recovered well and returned to work a few months later.
Tommy said: "I never thought I'd have to ring family to tell them this. I thought he'd go to hospital and survive."
Andrew grew up in Bridgend and owned his own business - a sewing shop for 30 years.
He later decided to close the business and went to university to study fashion.
The pair were in a relationship for two and a half years, time Tommy described as "the best time of my life."
"We never argued, he never called me any names and he'd bring me 20 coffees in a day when I was working.
"Everyone loved him and was always thinking of other people."
He added: "Andrew was loved by everyone"
Tommy is now raising money for the British Heart Foundation in memory of Andrew and says friends can pay their respects when Andrew's body is driven past their house on the Taffs Mead Embankment on Tuesday March 30 at 12.20pm, the day of his funeral.
His colleagues at St David's Hall have also paid tribute.
Front of house manager at St David’s Hall, Debbie Williams said: "Andy came to work at St David’s Hall as house manager in 2017 and to say he took to it like a duck to water would have been an understatement.
"His enthusiasm was infectious and he was a person who adored his work – particularly the high-profile events such as Bafta Cymru, Cardiff Singer of the World and the National Police Memorial Day to name but a few.
"He was an extremely professional, well-respected and popular member of, not only the Front of House team, but every department within St David’s Hall.
"Andy’s ambition was to expand his role as house manager and he was involved with projects to assist what would have been a natural and deserved progression.
“To say someone has gone before his time is probably a hackneyed cliché but the saying should have been made for Andy. His sudden death has sent shockwaves through the Hall and has had a huge impact on his friends and colleagues."
Mike Pope, TTP all-Wales surge team manager, added: "We are all truly shocked and saddened by Andrew’s passing. He was a fantastic person and made such an impact with us here on Test Trace and Protect.
"Andrew was helpful, friendly and superb at the job. He is going to be very sorely missed."
To donate to the fundraiser click here.
