Following the discovery of Mrs Rausing's body, her husband who had initially been detained for drug possession, was rearrested in connection with her death and held in custody at a South London police station.
After being moved from a police station on Tuesday night, authorities said he was "currently receiving medical attention" at an undisclosed "facility".
Within hours of the discovery of the body, police seized security CCTV footage from inside and outside the property focusing on Cadogan Place and a mews at the rear.
The news was reportedly broken to his 86-year-old father Hans Rausing and his wife Marit at their 900-acre East Sussex estate.
Mrs Rausing and her 49-year-old husband have both fought lengthy battles with drug addiction, having first met while attending a rehabilitation clinic in the United States in the early 1990s.
In recent weeks, the couple have been seen out walking in the area. Mr Rausing, looking gaunt and frail, often wore a baseball cap while his wife wore cut-off trousers and open-toed sandals.
A spokesman for Scotland Yard said: "On Monday 9 July a 49-year-old man was arrested on suspicion of possession of drugs. Following a subsequent search of an address in Cadogan Place SW1, a body was found.
"The death is being treated as unexplained. We believe we know the identity of the deceased but await further confirmation The man was further arrested in connection with the death and is currently in custody at a south London police station."
Mrs Rausing, who was born Eva Kemeny, is the daughter of a wealthy Pepsi Cola executive .
The Kemeny family live on Hilton Head Island, an idyllic spot off South Carolina known for it's beaches and annual wine tasting festival.
Mrs Rausing's younger sister Be Kemeny, who used to be married to Jack Kidd, the polo playing brother of model Jodie Kidd, lives in a beach house on the island with her children.
In a statement issued on Tuesday night, her parents, Tom and Nancy Kemeny, said that "along with all of their family are deeply saddened by the death of their beloved daughter, Eva Louise Rausing".
They added: "Eva was a devoted wife for twenty years and mother of four much loved and wonderful children.
"During her short lifetime she made a huge philanthropic impact, supporting a large number of charitable causes, not only financially, but using her own personal experiences. She bravely fought her health issues for many years.
"The family is devastated at her death and asks to be given privacy at this difficult time."
Mr Rausing's family, who established the Swedish Tetra Pak drinks carton empire, are worth an estimated £4.5 billion and were last year ranked as Britain's 12th richest in the Sunday Times Rich List.
Mr Rausing and his wife shared their time between London and Barbados, where they own an 11 bedroom beachfront mansion worth £15 million.
They have four children, aged between 11 and 17, who attend a private school in East Sussex.
The school is 25 minutes away from the 900-acre estate in Wadhurst, East Sussex, where their grandfather Hans, the patriarch of the Rausing dynasty, lives.
He moved to Britain in 1980 in order to escape Sweden's punitive tax laws but is reputed to live modestly, doing his own cooking and driving a Morris Minor car around the local village.
Mr Rausing, who is known to his friends as Hans K to differentiate himself from his father, did not enter the business world and instead travelled to India where it is thought he first experimented with drugs.
After meeting his wife in a clinic in the United States, the pair moved to London and set up home in Chelsea.
They have both donated millions to charity and have lent their support to several organisations that support people struggling with addiction.
The couple have worked on a number of charitable initiatives with the Prince of Wales, who once described Mr Rausing as "one very special philanthropist".
A spokesman for the charity Action on Addiction, which has long enjoyed Mrs Rausing's support said: "Everyone involved with Action on Addiction is devastated to hear the news of Eva Rausing's untimely death.
"Without any desire for public recognition, Eva has, through her wonderfully generous support of this and other charities helped so many people for over 20 years. We offer our deepest sympathy to Eva's family at this time of great loss."
The couple moved into their five-storey mansion after selling another property near-by for £12.65m six years ago.
Neighbours in the multimillion pound homes in Cadogan Place said they rarely saw the Rausings and sometimes wondered if the house was occupied apart from a Filipino maid.
Elizabeth Caldeira, a housekeeper for an Iranian family, said she when she saw the police arrive at the Rausing property she had believed there had been a break in.
Mr Rausing has two sisters Lisbet and Sigrid, who both live in Holland Park, west London.
Lisbet is a successful historian, while Sigrid is a human rights activist, who funds a number of charitable foundations.
In a statement his parents, Hans and Märit Rausing, together with their relatives said: "Hans and Märit Rausing and their family are deeply shocked and saddened to hear of the tragic death of their daughter-in-law Eva Louise Rausing.
"They ask that their privacy be respected at this sad time."
