Updated: 12 APR 21 12:35 ET

By Eric Levenson and Aaron Cooper, CNN

(CNN) -- An expert cardiologist testified Monday that George Floyd died from cardiopulmonary arrest caused by low oxygen levels brought on by prone restraint and positional asphyxia -- making him the fifth doctor to say as much in Derek Chauvin's trial.

Dr. Jonathan Rich, a cardiologist based in Chicago, testified that Floyd's heart was unable to get enough oxygen because of of how he was restrained. His review of the medical records, videos and autopsy also rejected other causes of death due to drugs or heart issues, as the defense has suggested.

"George Floyd did not die from a primary cardiac event and he did not die from a drug overdose," said Rich.

"I believe that Mr. George Floyd's death was absolutely preventable," he added.

The comments came Monday at the beginning of the third week of testimony as Minnesota prosecutors neared the end of their case against former Minneapolis Police officer Chauvin. A member of Floyd's family as well as another policing expert are still expected to testify before the prosecution gives the defense the opportunity to call witnesses, which could come as early as Monday afternoon.

Judge Peter Cahill noted he expects closing arguments in the case next Monday.

The doctor's testimony follows a series of medical experts who testified last week that Floyd died last May because of Chauvin's restraint. On Friday, the medical examiner who conducted Floyd's autopsy noted that Floyd's history of hypertension and the fentanyl and methamphetamine in his system played a role in his death, but they were not the direct cause.

"In my opinion, the law enforcement subdual, restraint and the neck compression was just more than Mr. Floyd could take by virtue of those heart conditions," Dr. Andrew Baker said.

Chauvin, 45, has pleaded not guilty to second-degree unintentional murder, third-degree murder and second-degree manslaughter charges.

Defense attorney Eric Nelson has focused on three arguments he says will acquit Chauvin: Floyd died of drug and health problems, Chauvin's use of force was ugly but appropriate, and the crowd of bystanders became hostile and distracted Chauvin from taking care of Floyd. Witnesses called by the prosecution have contested each of those theories -- but it will be up to the jury of five men and nine women to ultimately decide.

While the trial has focused on Chauvin and Floyd, the societal stakes of the high-profile case were made vividly clear on Sunday when police shot and killed a Black man following a traffic stop in the Minneapolis suburb of Brooklyn Center.

In response, protesters gathered Sunday evening and marched toward the police department, and the city's mayor described "growing civil unrest." The state deployed the Minnesota National Guard after reports of a number of break-ins.

What the prosecution has said so far

The doctor's medical testimony will further the third of three phases in the prosecution's case against Chauvin.

The first week of testimony largely focused on Floyd's final moments and the distressed bystanders who watched Chauvin kneel on Floyd's neck and back for over 9 minutes while he was handcuffed and prone on the street. Video from the bystanders and police body camera footage showed Floyd's gasps for air and calls for his "mama" over those excruciating minutes.

Early last week, prosecutors called a series of police supervisors and use-of-force experts who criticized Chauvin's actions. They said he violated policies around de-escalation, objectively reasonable use of force and the requirement to render aid. Foremost among the critics was Minneapolis Police Chief Medaria Arradondo.

"That in no way shape or form is anything that is by policy. It is not part of our training, and it is certainly not part of our ethics or our values," Arradondo said.

The medical testimony on Thursday and Friday, particularly from Dr. Martin Tobin, laid out the mechanics of how Floyd died. The renowned pulmonary critical care doctor testified Thursday morning that Floyd died from a "low level of oxygen" when Chauvin pinned him to the street and restricted his ability to breathe.

Floyd's preexisting health conditions and drug use were not relevant to his death, Tobin said.

"A healthy person subjected to what Mr. Floyd was subjected to would have died," he said.

Judge rejects call to sequester jurors

In a pre-court hearing Monday, Nelson asked the court to question jurors further about what they had heard about the police shooting in Brooklyn Center and asked to sequester them for the rest of the trial.

"This incident, while I understand it's not this case, I understand that it does not involve these same parties, but the problem is the emotional response that case creates sets the stage for the jury to say 'I'm not going to vote not guilty because I'm concerned about the outcome,'" he said.

The state opposed the motion for sequestering them, saying it would not be appropriate or effective.

"We can't have every single world event that might affect somebody's attitude or emotional state or anything be grounds to come back and re-voir dire all the jurors," prosecutor Steve Schleicher said.

Judge Peter Cahill rejected the defense's request to sequester or question jurors. He said he plans to fully sequester the jury during deliberations, as he originally ordered last year. Jurors in the trial are currently partially sequestered, meaning they are released to go home each day.