MINNEAPOLIS: The attorney for Derek Chauvin began his defence of the former Minneapolis police officer on Tuesday, calling his first witnesses in an effort to sow doubt in the minds of the jury over what caused the death of George Floyd.

Chauvin, 45, is charged with murder and manslaughter and the most compelling evidence against him is bystander video which shows him kneeling on the neck of a handcuffed Floyd for more than nine minutes.

Eric Nelson, Chauvin's lawyer, has adopted what amounts to a three-pronged defence strategy during the opening weeks of the high-profile trial.

Drugs and health conditions

The cause of death of the 46-year-old Floyd is central to the case against Chauvin with prosecutors saying he died from asphyxia, or a lack of oxygen, and the defence claiming it was drugs or heart disease.

"The evidence will show that Mr Floyd died of a cardiac arrhythmia that occurred as a result of hypertension, his coronary disease, the ingestion of methamphetamine and fentanyl, and the adrenaline flowing through his body, all of which acted to further compromise an already compromised heart," Nelson said in his opening statement.

The first witness called by the defense on Tuesday was a retired police officer who was involved in a traffic stop of Floyd a year before his death.

A paramedic who was called to the scene of the May 2019 incident also testified and told the jury Floyd admitted having taken opioids.

Another witness appeared under subpoena by the defense: Shawanda Hill, a woman who was with Floyd on the day of his May 25, 2020 arrest.

Hill said Floyd had been "happy, normal, talking, alert" and then fell asleep in his car.

She said she tried to wake him a "couple of times" and he eventually woke up when police arrived in response to a report that Floyd had used a counterfeit $20 bill.

Prosecutors have acknowledged that Floyd had fentanyl and meth in his system at the time of his death but introduced testimony from several medical experts who said the doses were not lethal.

Andrew Baker, the chief medical examiner who conducted the autopsy, said Floyd had heart disease and had consumed drugs but they were not the "direct causes" of his death.

Baker said Floyd's cause of death was "restraint and neck compression" while being subdued by police.