Police guard the Rausing residence in London tonight.
Scotland Yard said the death was being treated as unexplained.
A post-mortem examination began at 1pm today at Westminster Mortuary.
A Scotland Yard spokesman said: "We believe we know the identity of the deceased but await further confirmation."
- Tetra Pak is one of the world's leading companies for food processing and packaging solutions.
- Deliver services to people in more than 170 countries.
- The company has close to 22,000 employees, based in 85 countries.
- Tetra Pak is one of three companies in the Tetra Laval Group – a private group that started in Sweden. The other two companies are DeLaval and Sidel.
Police say a 49-year-old man was initially arrested on suspicion of being in possession of drugs but after the discovery of a woman's body, was further arrested in connection with her death.
A post-mortem examination has taken place this afternoon.
A body, believed to be that of the wife of Tetra Pak heir Hans Rausing, has been found in a flat in Belgravia, London.
Police say they are treating Eva Rausing's death as "unexplained".