BBC ON THIS DAY | 16 | 1977: Rock and roll 'king' Presley dies1977: Rock and roll 'king' Presley diesElvis Presley, whose singing and style revolutionized popular music in the 1950s, has died.
Presley, 42, was discovered slumped in a bathroom at his mansion in Memphis, Tennessee on Tuesday.
He was rushed to the Baptist Memorial Hospital in Memphis but was pronounced dead on arrival.
The Tennessee state pathologist, Dr. Jerry Francisco, said a post mortem examination of the singer's body had revealed he died of cardiac arrhythmia - a form of heart attack.
"The precise cause has not yet been determined for the cardiac arrhythmia," Dr Francisco said.
"It may take several days to several weeks to determine that specific cause and in some cases it never is determined."
The three-hour examination uncovered no sign of any other diseases or any drug abuse, Dr Francisco added.
Presley was divorced from his wife Priscilla in 1973 but it was rumoured that he had recently become engaged to Ginger Alden, 20.
She was reportedly spotted wearing a $50,000 (£20,315) diamond engagement ring from Presley.
Ms Alden and other members of his entourage were at Graceland when he collapsed.
There had been indications of Elvis Presley's declining health for some time.
Earlier this year the singer had cancelled several performances in Louisiana and returned to Memphis suffering what his doctors termed "exhaustion".
No arrangements have been announced yet for his funeral which is scheduled for Friday.