Georgian businessman Badri Patarkatsishvili died of natural causes, according to initial post-mortem test results released by British police.
Mr Patarkatsishvili, 52, had been accused of fomenting a coup in the ex-Soviet republic.
He collapsed and died on Tuesday at his home in Leatherhead, south-west of London.
Police say that toxicology tests still have to be completed and the results of those will not be available for a number of weeks.
The toxicology tests are a routine part of the post-mortem examination.
Police said late yesterday that they had found no traces of radioactivity after forensics experts spent all day studying the scene at the tycoon's plush home.
Some friends have voiced surprise at the claim that Mr Patarkatsishvili had died from a heart attack saying he had not been reported to be in poor health.
The case has triggered memories of the death by radioactive poisoning of Kremlin opponent Alexander Litvinenko in 2006, which hit diplomatic ties between London and Moscow.
The flamboyant businessman, recognisable by his big white moustache, was Georgia's richest man.
He was a major force behind an opposition movement that took to the streets in the Georgian capital Tbilisi last November, prompting a violent police crackdown.
Pro-Western President Mikheil Saakashvili's government accused Mr Patarkatsishvili, who lived mostly in Britain and Israel, of attempting to mount a coup.
