Maryland’s former chief medical examiner testified for Derek Chauvin’s defense on Wednesday that George Floyd died due to his underlying heart disease — not the police restraint.

“In my opinion, Mr. Floyd had a sudden cardiac arrhythmia, or cardiac arrhythmia, due to his atherosclerosis and hypertensive heart disease … during his restraint and subdual by the police,” said Dr. David Fowler, a forensic pathologist.

Floyd had narrowed coronary arteries, known as atherosclerosis, and an enlarged heart due to his high blood pressure, or hypertension, Fowler said. Floyd’s fentanyl and methamphetamine use and a tumor known as a paraganglioma were other significant conditions that contributed to his death, he said.

Fowler also put forth a novel argument that carbon monoxide from the squad car’s exhaust may have contributed to his death.

In all, he said Floyd’s death should have been classified as “undetermined,” rather than a homicide, because there were so many competing causes.

The testimony cuts at the prosecution’s argument, bolstered by five separate medical experts, that Floyd’s primary cause of death was Chauvin’s restraint of a handcuffed Floyd in the prone position — known as “positional asphyxia.” To get a guilty verdict, prosecutors have to prove that Chauvin’s actions were a “substantial causal factor” in Floyd’s death.