Fine, suppose Floyd had a cardiac event because he took PCP.
When someone becomes unresponsive, you roll him on his back, check for a pulse, start CPR, get the defibrillator and oxygen out of the squad car.
You do not keep kneeling on a dying man’s neck. Chauvin was a cop long enough to recognize unresponsiveness.
An old principle of law: you take your victim as you find him. Punch a little old man in the belly to rob him and he dies of a heart attack, you have just committed homicide. Kneel on the neck of a man who is telling you he is having difficulty breathing, keep on doing that after he loses consciousness. A jury would reasonably find your actions contributed to his death, especially if you have an affirmative duty to act: i.e. you are an officer with the man in your custody and control.
You make a good point. That is why I want to see the autopsy and video that shows why the police officers got on top of this guy in the first place. Was he flailing uncontrollably? Did they think he was a danger to himself or others? It is somewhat puzzling the three officers would be on top of this guy while he is handcuffed if all he was doing was refusing to get into the police vehicle. Again, I would be lying if I said I knew the answer to all of these questions.