An "extremely fit" father suddenly collapsed after having a mystery allergic reaction, an inquest was told.
Alistair Henden, 56, died after a trip to a DIY store to buy supplies, including tile adhesives.
A medical examination showed he had an allergic reaction, but none of the canisters were open and doctors were at a loss at what caused it.
His devastated wife Caroline told proceedings the day had started like any other and that her husband had slept in as he did not start work until the afternoon.
She said he was a keen gardener who enjoyed DIY and was "extremely fit".
Mr Henden, a part-time school caretaker from Bath, collapsed when he got home from the trip to the DIY store and was found by his daughter Lydia who called 999.
Paramedics quickly arrived, as did colleagues in a helicopter, but he was declared dead at the scene.
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PC Leigh Watts from Avon and Somerset Police attended the address on August 18 and told proceedings both women were "extremely upset and in disbelief".
Dr Arun Gadhok, Mr Henden’s GP, confirmed his patient had no known medical conditions or a history of allergic reactions.
During a post-mortem examination carried out at Flax Bourton, Dr Edward Sheffield found that all the valves in Mr Henden's heart were normal and his coronary arteries were free from any blockage.
He said he found the cause of death was a "sudden cardiac failure" in a normal heart and suggested it was a case of adult death syndrome.
Blood tests taken later by Dr Sarah Johnston, consultant immunologist for the North Bristol NHS Trust, found he had significantly raised levels of mast cell tryptase which she suggested indicated anaphylaxis following an allergic reaction.
But she could not tell what had caused it.
Dr Peter Harrowing recorded a short narrative conclusion, adding: “Alistair died of a sudden cardiac failure due to an allergic reaction of unknown cause.
“I would like to take this opportunity to extend my condolences to his friends and family.”