An autopsy report revealed that a pet Gila monster’s venomous bite contributed to a Colorado man’s death in February in what an expert described as “an incredibly rare” fatality caused by one of the desert lizards.

The man, Christopher Ward, 34, died on Feb. 16 “due to complications of Gila monster envenomization,” said the Jefferson County Coroner’s Office autopsy report, which also cited heart and liver problems as contributing factors.

Mr. Ward endured a four-minute-long bite by the lizard to his right hand on the night of Feb. 12, the report said. He lapsed in and out of consciousness for about two hours before seeking medical attention, the report said.

Paramedics found Mr. Ward in a bed, minimally responsive and “in apparent severe distress,” the report said. He was taken to a hospital, where he was put on life support and “continued to decline throughout his hospitalization.”

Mr. Ward’s girlfriend, who was present the night of the bite and who called 911, told the authorities in Lakewood, a suburb of Denver, that she was in another room when Mr. Ward was bitten and did not know what caused the lizard to strike.

She said she had heard him say something “and it ‘didn’t sound right,’” according to an animal control officer’s report. When she entered the room, she found the lizard “latched” onto Mr. Ward, the report said.