The “number one suspect” in the death of a wealthy Russian whistleblower is seafood he ate during a romantic meal with his lover in Paris, an inquest heard.
But a “malignant” poisoner at the smart Japanese restaurant could also be to blame, it was claimed.
Alexander Perepilichnyy, 44, collapsed while out jogging near his home in Weybridge, Surrey, in November 2012.
The married father had spent the night before with his ex-model girlfriend Elmira Medynska, 28, at the Buddha Bar in Paris.
The Old Bailey has heard he sent back “bad” tempura prawn and ate either sushi or sashimi then vomited repeatedly when he got back to his hotel.
Giving evidence on Wednesday, Ms Medynska said: “I think maybe he vomited because it was not good food in the restaurant.”
Coroner Nicholas Hilliard QC is examining how Mr Perepilichnyy died, whether he was poisoned and who might have had a motive for murder.
The inquest heard from a cardiologist on the effects of fish poisoning on the heart.
Dr Peter Wilmshurst said histamine or scombroid poisoning could result from eating long distance fish, such as salmon, tuna and mackerel.
Symptoms include rashes, hives cramps, vomiting, a “peppery taste” and itching.
Dr Wilmshurst, who had suffered fish poisoning himself, said: “It’s rarely fatal. There are cases of people who have died of it.”
On the effect on the heart, he said: “It can do all sorts of things to the heart.
“It often causes the heart rate to go fast. Histamine has direct effects on the heart.”
The cardiologist said he was aware of a case of an Australian mother and daughter who died in Bali.
Peter Skelton QC, counsel for the coroner, said: “Ms Medynska’s evidence was he may have eaten some kind of fish on the night of November 9.
“She could not be clear about it. They did not share their food. He said at the time some of the food tasted bad and sent it back. It could have been prawns rather than fish.
“What she was clear about was that he vomited three times during the course of an hour and she also said that afterwards when he returned from the bathroom he had a red face and red eyes.
“He said he felt better afterwards and did not want to go to see a doctor.”
Dr Wilmshurst said there was a “more than 50%” chance it was poisoning, if he ate fish at the Japanese restaurant.
Asked if that contributed to his death, he said: “If one accepts he had scombroid fish poisoning that night then dies the next day having had a condition 18 hours earlier.
“If you cannot find any other reason, that becomes the number one suspect.”
But he added: “The big problem is there are so many unknowns.”
Bob Moxon Browne QC, for Legal and General Assurance, suggested there were three possibilities, including “malign” intent.
He said: “It seems likely that Mr Perepilichnyy ate something that disagreed with him on the night before his death.
“That could have been because someone malignantly put poison in his food.”
The expert said he could not say as he was not a toxicologist.
Mr Moxon Browne went on: “Another is, he had scombroid fish poisoning and there is a further possibility which is he simply contracted some form of food poisoning that did not have a histamine base.”
John Beggs QC, for the family, suggested that Mr Perepilichnyy was used to “fine dining” and would know if food was “not right”.
He pointed out that he did not “make love” with the former model at the five-star Bristol hotel that night, which would be consistent with him having fish poisoning.
The witness said: “It’s sufficiently like it – I thought I ought to raise it as a possibility for the court to consider.”
Mr Beggs asked if a Viagra-like substance, which was found in Mr Perepilichnyy’s body, could affect the heart.
Dr Wilmshurst said it could.
Professor Robin Ferner said he first thought of the plant alkaloid Colchicine when he looked for a delayed-action poison which causes vomiting in the way described by Ms Medynska, although none was identified in the body.
The toxicologist did not agree that fish poisoning caused Mr Perepilichnyy to suffer a fatal cardiac arrhythmia, although nothing could be ruled out.
He told the court that while tests for poisons had been “extensive” they had not been “exhaustive”.
Fiona Barton QC, for Surrey Police, said: “You have posited a number of possibilities that arise from the evidence that is available and none of those possibilities are in your view likely.”
Prof Ferner said: “That’s true. The question is not whether they are likely, it’s whether they are more likely than an independent cardiac cause.”
He refused to say if a heart problem was “more likely than not” the cause of death, and there was laughter in court as he added: “If I could, that would be helpful to proceedings.”
Dr Geoffrey Kite, from Kew, first raised the possibility that an unknown compound in Mr Perepilichnyy’s body could be the poisonous plant gelsemium – otherwise known as heartbreak grass.
But testing ruled it out “beyond reasonable doubt”, he said.