Nilsen – who is believed to have killed as many as 15 young men – died in hospital in York aged 72 on Saturday after serving 34 years of a whole life sentence.
The serial killer, who was an inmate at Full Sutton Prison in East Yorkshire, was taken to York District Hospital on 10 May after complaining of stomach pains, an inquest at Hull Coroners Court heard yesterday.
Coroner’s officer Gary Lynch said Nilsen was found to have a ruptured abdominal aortic aneurysm which was repaired, but he then suffered an blood clot as a complication of the surgery.
Mr Lynch said Nilsen died on 12 May after his condition deteriorated.
He said that a subsequent post-mortem examination showed that the mass murderer’s immediate cause of death was pulmonary embolism and retroperitoneal haemorrhage.
He said the underlying causes of this were deep vein thrombosis and “abdominal aortic aneurysm rupture repair”.
East Riding of Yorkshire coroner Professor Paul Marks said that, as Nilsen’s family had not requested a second post-mortem examination be performed, the body could be released.
He said: “I’m happy to sign the paperwork for Dennis Nilsen’s body to be returned to his next of kin for funeral arrangements to be made.”
Prof Marks adjourned the brief hearing, saying a date for the full inquest had yet to be fixed.
Nilsen became known as the Muswell Hill murderer after he a killing spree in the late 1970s and early 1980s.
He is believed to have killed as many as 15 men, most of them homeless homosexuals, at his north London home.
After luring his victims to their death, Nilsen would often sit with their corpses in his home for several days before dismembering them.
His crimes were only detected by chance, when a drain outside his home on Cranley Gardens, Muswell Hill, became blocked by human remains he had tried to flush away.
He was jailed for life with a recommendation he serve a minimum of 25 years in 1983, after being found guilty of six counts of murder and two of attempted murder.
The sentence was later upgraded to a whole-life tariff.
Nilsen’s home in Muswell Hill has been on the market several times since his crimes were discovered, and is still occupied today, with flowers visible in the attic window.
A spokesman for the Prison Service said earlier this week that, as with all deaths in custody, there will be an independent investigation by the Prisons and Probation Ombudsman.
Nilsen was born and grew up in Fraserburgh, Aberdeenshire. He met his victims, all of them men, in a pub and he would take them back to his flat for a drink. Most were homeless, some were homosexuals and some were prostitutes.