The Los Angeles County medical examiner said Breitbart suffered focal coronary atherosclerosis, or hardening of the arteries, the Los Angeles Times reported. The immediate cause of death was heart failure.
The coroner said Breitbart's blood-alcohol level was 0.04 percent and there was no trace of illegal drugs in his system. The death was ruled a natural one.
Breitbart was 43 when he collapsed in the Westwood neighborhood of Los Angeles March 1. He was pronounced dead a short time later at the UCLA medical center.
After working on the Drudge Report and helping start Huffington Post, Breitbart founded his own site in 2005, Breitbart.com, saying it was dedicated to the destruction of the "institutional left." One of its best-known actions was a 2009 sting by right-wing filmmaker James O'Keefe on that led to the demise of the left-wing community advocacy group ACORN.
Breitbart grew up in Los Angeles, married the daughter of actor Orson Bean and lived in Westwood with his wife and four children.