The preliminary results of an autopsy in the Netherlands on Slobodan Milosevic show the former Yugoslav leader died of a heart attack.
A toxicological report on the body has still to be completed amid allegations he may have died of poisoning.
Serbian President Boris Tadic has ruled out a state funeral for Mr Milosevic.
He also said there would be no pardon for the former leader's wife, Mirjana Markovic, who faces abuse of power charges and is now in exile in Moscow.
Mr Milosevic was found dead in his cell on Saturday in The Hague where he was on trial for war crimes.
An official for the UN tribunal said that his remains would be released on Monday to his family.
The tribunal said that the full autopsy report might take more than a day to be released but that the preliminary results showed Mr Milosevic had died of a "myocardial infarction", the medical term for a heart attack.
Mr Milosevic, 64, had been suffering from two heart conditions, it added, without naming them.
Slobodan Milosevic feared he was being poisoned just a day before he died in his cell, according to lawyer Zdenko Tomanovic.
He had complained of "strong drugs in his system only used for treating leprosy or tuberculosis" in a letter to Russian Foreign Minister Sergei Lavrov.
Mr Milosevic had, he said, been citing a medical report from 12 January.
Mr Milosevic had requested permission to travel to Moscow for medical treatment but the tribunal refused, fearing that he might not return to The Hague.
Dutch public television NOS reported on Sunday that a blood sample taken from Mr Milosevic some time between November and January had shown traces of drugs often used to treat leprosy or tuberculosis.
They may have neutralised the medicine Mr Milosevic was taking for high blood pressure and heart problems, it said, quoting an unidentified tribunal "adviser".
Sources close to the court suggest Mr Milosevic may have deliberately mixed or missed the dosages for his bad heart and high blood pressure.
Tribunal ploughs on
UN chief prosecutor Carla del Ponte said Mr Milosevic's death made it even more urgent for Serbia to arrest the most wanted Bosnian Serb war crimes fugitives, Ratko Mladic and Radovan Karadzic.
Mr Milosevic had been held at the UN war crimes tribunal since 2001.
He was on trial on charges of war crimes and crimes against humanity for his alleged central role in the wars in Bosnia, Croatia and Kosovo during the 1990s.
He also faced genocide charges over the 1992-95 Bosnia war, in which 100,000 people died.
Correspondents say the tribunal's monitoring of inmates is under scrutiny because Mr Milosevic's death came within a week of the suicide of a former rebel Croatian Serb leader, Milan Babic.
Both Mr Milosevic's widow Mirjana Markovic and son Marko have blamed the tribunal for his death.
CHARGES AGAINST MILOSEVIC
Genocide, relating to the massacre in Srebrenica, Bosnia
Crimes against humanity, relating to Bosnia, Croatia and Kosovo
Grave breaches of the Geneva Conventions, relating to Bosnia and Croatia
Violations of the laws or customs of war, relating to Bosnia, Croatia and Kosovo
They are living in Moscow and both face fraud charges in Serbia.
Mr Milosevic's daughter Marija, now living in Montenegro, would also face criminal charges in Serbia.
There are reports that his family is divided over whether he should be laid to rest in Serbia, his birthplace Montenegro, or in Russia.
A BBC correspondent in the Hague says that delicate negotiations may be expected behind the scenes, and the government can't afford to alienate the former president's nationalist supporters.