The coroner's report says the 38-year-old died from "community-acquired pneumonia" along with lung, heart and blood vessel problems.
Low levels of eight drugs, including both over-the-counter and prescription medications, were found in Haim's system along with some marijuana. However, the coroner's office said the drugs were not a factor in his death.
"He had some blockages of the heart and the artery, and he died of natural causes. There were a number of prescription drugs found in his system, but not to a lethal level," said Los Angeles coroner's spokesperson Ed Winter.
The drugs included tranquilizers and some common cold and flu medications -- such as ibuprofen, the cough-suppressant dextromethorphan; the antihistamine diphenhydramine; carisoprodol, a prescription muscle relaxant; the tranquilizers diazepam and meprobamate, which are found in Valium and other medications; and the antidepressants fluoxetine and olanzapine
Haim, who struggled with drug problems throughout his life, died March 10 after collapsing in the apartment he shared with his mother in the 3600 block of Barham Boulevard in Universal City. He had been suffering from flu-like symptoms, and police said he was taking over-the-counter and prescription medications.
The coroner's report noted that Haim's heart was abnormally large and factored in his death.
"His heart was 530 grams. The average normal heart weighs 300 grams," coroner's spokesman Craig Harvey said.
Haim also had damaged lungs and arteriosclerosis of his coronary arteries, with some vessels 50-percent and even 75-percent blocked. Haim also had an enlarged liver.
At the time of his death, police said the Canadian actor may have died an overdose, but no illegal drugs were found at the apartment. However, the coroner found his name on prescriptions from nearly two dozen doctors.
California Attorney General Jerry Brown said in April that Haim's death had been linked to an illegal and massive prescription drug ring. He said an unauthorized prescription in the actor's name was found during a probe of phony prescription pads ordered from a San Diego vendor.
Brown said Haim employed "doctor shopping" to obtain 553 prescription pills - including powerful sedatives such as Valium and Xanax and painkillers such as Vicodin and Oxycontin - in the two months before his death. He called Haim a poster child for prescription drug abuse.
However, no Oxycontin was found in his body.
Haim was born in Toronto in 1971. He earned fame for roles in the 1980s films "The Lost Boys," "Lucas," and "License to Drive." He had just finished a shooting a movie and was trying to get his career back on track when he died.
The Associated Press contributed to this report.