THE defence at the murder trial of former officer Derek Chauvin over the death of George Floyd wrapped up its case yesterday without putting Chauvin on the stand.

Chauvin informed the court that he would not testify, saying he would invoke his Fifth Amendment right not to take the stand.

“Is this your decision not to testify?” Judge Peter Cahill asked.

“It is, your honour,” Chauvin said.

Closing arguments are set for Monday, after which the jury will begin deliberating.

The decision not to testify was announced a day after a forensic pathologist testifying for the defence said that Floyd died of a sudden heart rhythm disturbance as a result of his heart disease.

That contradicted prosecution experts who said Floyd succumbed to a lack of oxygen from the way he was pinned down.

Dr David Fowler, a former Maryland chief medical examiner who is now with a consulting firm, said on Wednesday the fentanyl and methamphetamine in Floyd’s system, and possibly carbon monoxide poisoning from a car exhaust, were contributing factors in the 46-year-old black man’s death last May.

“All of those combined to cause Mr Floyd’s death,” he said.

Fowler also testified that he would classify the manner of death “undetermined”, rather than homicide, as the county’s chief medical examiner ruled.

He said Floyd’s death had too many conflicting factors, some of which could be ruled homicide and some that could be considered accidental.

Chauvin’s lawyer Eric Nelson is trying to prove that the Minneapolis police veteran did what he was trained to do and that Floyd died because of illegal drug use and underlying health problems.

Prosecutors say Floyd died because the white officer’s knee was pressed against Floyd’s neck or neck area for nine-and-a-half minutes as he lay on the pavement on his stomach, his hands cuffed behind him.

Fowler listed a multitude of factors or potential ones: Floyd’s narrowed arteries, his enlarged heart, his high blood pressure, his drug use, the stress of his restraint, the vehicle exhaust and a tumour or growth in his lower abdomen that can sometimes play a role in high blood pressure by releasing “fight-or-flight” hormones.

Fowler said all of those factors could have acted together to cause Floyd’s heart to work harder, suffer an arrhythmia or abnormal rhythm, and suddenly stop.

Prosecutor Jerry Blackwell launched an aggressive cross-examination, attacking Fowler’s findings. He got Fowler to acknowledge that even someone who dies from being deprived of oxygen ultimately dies of an arrhythmia.

A number of medical experts called by prosecutors have said Floyd died from a lack of oxygen because his breathing was constricted by the way he was held down.

A cardiology expert rejected the notion that Floyd died of heart problems, saying all indications were that he had “an exceptionally strong heart”.

But Fowler said that Chauvin’s knee on Floyd was “nowhere close to his airway” and that Floyd’s speaking and groaning showed that his airway was still open.

He also testified that Chauvin’s knee was not applied with enough pressure to cause any bruises or scrapes on Floyd’s neck or back.

Chauvin, 45, is charged with murder and manslaughter over Floyd’s death after his arrest on suspicion of passing a counterfeit $20 note at a neighbourhood market.