Under questioning by prosecutor Jerry Blackwell, Langenfeld said that based on the information he had, death by asphyxiation was "more likely than the other possibilities". Last June, he called it "murder".
Footage of Mr Chauvin, who is white, kneeling on African-American Mr Floyd's neck for more than nine minutes a year ago sparked global protests against racism.
Mr Chauvin, 45, has denied multiple charges of murder and manslaughter.
Chauvin attorney Eric Nelson questioned Langenfeld about whether some drugs can cause hypoxia, or insufficient oxygen. An autopsy found fentanyl and methamphetamine in Floyd's system. Chauvin's lawyers have said he followed his training and that Floyd died because of a drug overdose. A summary report listed fentanyl intoxication and recent methamphetamine use under "other significant conditions" but not under "cause of death".
He said a lack of oxygen was the most likely reason Floyd's heart had stopped beating. A narcotics antidote such as Narcan also does not help once someone is in cardiac arrest, Langenfeld said.
Officers carry tourniquets and are trained how to use them to treat gunshot wounds, they are taught how to do chest compressions, and they are given naloxone inhalers that can be used to rapidly reverse an opioid overdose, Arradondo said.
Floyd had been in cardiac arrest before arriving at the hospital and doctors worked on him for roughly half an hour after his arrival.
The video touched off protests against racial injustice and police brutality in the United States and around the world.
"It's well known that any amount of time that a patient spends in cardiac arrest without immediate CPR markedly decreases the chance of a good outcome", he told the jury. He said there is an approximately 10 per cent to 15 per cent decrease in survival for every minute that CPR is not administered.
The Associated Press reports that testimony on Monday will move toward Chauvin's training as a police officer.
Prosecutor Steve Schleicher noted that while some people may become more risky under the influence of drugs or alcohol, some may actually be "more vulnerable".
Floyd's girlfriend also took the stand last week, describing him as a kind man and a "mama's boy", but also a person who struggled with substance abuse.
Prosecutors have called Arradondo and other police officers to weaken Chauvin's defence that he did only what he was trained to do in his 19 years as a police officer. They also receive first-aid training, he said, adding, "And so, we absolutely have a duty to render that".
Officers kept restraining Floyd - with Chauvin kneeling on his neck, another kneeling on Floyd's back and a third holding his feet - until the ambulance got there, even after he became unresponsive, according to testimony and video footage. Langenfeld said while some of the symptoms may overlap, Floyd did not display signs of "excited delirium" which is commonly caused by drug use, he told the court, along with other factors.
The physician's appearance in court follows testimony from two paramedics who said that Mr Floyd had no pulse and did not appear to be breathing when they arrived at the scene.
The officers also rebuffed offers of help from an off-duty Minneapolis firefighter who wanted to administer aid or tell officers how to do it.
Minneapolis Police Inspector Katie Blackwell told jurors on Monday that former officer Derek Chauvin's restraint of George Floyd on May 25, 2020, did not fit the department's training in defensive maneuvers. He said that the restraint used against George Floyd wasn't necessary once he stopped resisting. "Chauvin knew what he was doing".
"It is my firm belief that the one singular incident we will be judged forever on will be our use of force".
Prosecutors highlighted video from Officer Thomas Lane's body camera on which he can be heard suggesting to Chauvin after Floyd lost consciousness that he be turned on his side, showing that Lane seemed to grasp the danger. A duty sergeant and a lieutenant who leads the homicide division both questioned Chauvin's actions in pinning Floyd to the ground. His sentiments similarly echoed Lt. Richard Zimmerman who called Chauvin's restraint on Floyd totally unnecessary in court on Friday.