Conservative blogger and commentator Andrew Breitbart died of heart failure stemming from coronary artery disease, Los Angeles County coroner's office officials said.
The 43-year-old collapsed as he was walking his dog near his Brentwood home and died on March 1.
Breitbart had a negligible amount of alcohol in his system, but no prescription or illicit drugs were found, said Craig Harvey, spokesperson for the coroner's office.
Harvey said foul play was not suspected and the case has been closed.
A conservative blogger and journalist, Breitbart helped launch the Huffington Post and was an editor at the Drudge Report.
He also founded his own news network, acting as the publisher of several news websites including Breitbart.com, Breitbart.tv, Big Hollywood, Big Government, Big Journalism and Big Peace.
Big Government broke an alleged ACORN scandal and also, in 2011, the "Weinergate" photo scandal that led to the resignation of New York Rep. Anthony Weiner.
Breitbert was known for publishing controversial exposes and wrote a best-selling critique of celebrity culture, "Hollywood, Interrupted." His newest book "Righteous Indignation: Excuse Me While I Save the World!" was on the New York Times bestseller list.