Pathologists said toxicological tests still had to be carried out to establish if the former Yugoslav president had died of natural causes.
Doctors said Milosevic may have died of his existing heart disease and associated problems like high blood pressure - but they will also examine whether the sudden death was caused by poison or a failure to take medicine prescribed for high blood pressure.
It already has been confirmed that a sample of blood taken from Milosevic in January contained a drug normally used to treat leprosy or tuberculosis and which could counteract other drugs used to treat Milosevic's high blood pressure.
Russian cardiac specialists said that doctors who treated Milosevic in the Netherlands suspected he had been secretly spitting out drugs given to him to treat his high blood pressure.
The UN war crimes tribunal in The Hague last night released a statement saying "Milosevic's cause of death was a 'myocardial infarction".
Dutch pathologists carried out an eight-hour post examination on the former Yugoslav president after he was found dead in his cell on Saturday.
Earlier, chief UN prosecutor Carla Del Ponte dismissed claims that 64-year-old Milosevic committed suicide or was poisoned as "rumours".
"You have the choice between normal, natural death and suicide," she told reporters at the tribunal, where Milosevic had been standing trial for more than four years on 66 counts of war crimes and genocide in Croatia, Bosnia and Kosovo during Yugoslavia's violent break-up in the 1990s.
Milosevic, branded the Butcher of the Balkans by critics, had suffered from heart ailments and high blood pressure, and his bad health caused numerous breaks in his 168 million trial. However, Milosevic's legal adviser said the former president had feared he was being poisoned.
He showed reporters a six-page letter Milosevic had written on Friday - the day before his death - claiming that traces of a "heavy drug" were found in his blood. The letter was addressed to the Russian Embassy asking for help.
Zdenko Tomanovic said Milosevic was "seriously concerned" he was being poisoned. "They would like to poison me," he quoted Milosevic as telling him.
A Dutch news report, citing an unidentified "adviser" to the UN war crimes tribunal, said traces of a drug used to treat leprosy and tuberculosis had been found in a blood sample taken from Milosevic in recent months.
Milosevic had appealed to the war crimes tribunal last December to be allowed to go to a heart clinic in Moscow for treatment. The request was denied. He repeated the request as late as last month.
Milosevic underwent frequent medical examinations by doctors and specialists appointed by the tribunal and by Serb doctors brought at his own request. Detailed reports were routinely submitted to the judges.