Hollywood actor Heath Ledger may have died from a heart attack not a drug overdose according to new reports.

The actor, who was filming in Battersea weeks before his death in his New York apartment, was found with six different types of drugs, including sleeping pills and anti-anxiety medication.

But a second round of tests appear to rule out a drug overdose, leading investigators to consider the Brokeback Mountain star could have died from a heart attack despite being just 28 years old.

The Australian actor was filming scenes for The Imaginarium of Dr Parnassus at Battersea Power Station just before Christmas.

Ledger's family held a private memorial service for him in Los Angeles on Saturday.

His body is expected to be flown back to his home city of Perth, Australia, for burial.