Andrew Breitbart, the conservative Internet publisher and blogger, died early this morning at age 43.
A statement posted on his website said that Breitbart died "unexpectedly from natural causes" this morning.
The Los Angeles Coroner's Office confirmed to ABC News Radio that Breitbart died shortly after midnight at UCLA Medical Center.
Breitbart was walking near his house in California's Brentwood neighborhood shortly after midnight when he collapsed, his father-in-law the actor Orson Bean told the Associated Press.
Someone who saw Breitbart fall called paramedics and revival attempts were made, the AP reports. He was taken to the emergency room at Ronald Reagan UCLA Medical Center in L.A.
"I don't know what to say. It's devastating," Bean told the AP.
Breitbart had apparently suffered heart problems a year ago, but Bean did not know what had happened.
The following statement was posted on Breitbart's website today:
"With a terrible feeling of pain and loss we announce the passing of Andrew Breitbart. We have lost a husband, a father, a son, a brother, a dear friend, a patriot and a happy warrior.
Andrew lived boldly, so that we more timid souls would dare to live freely and fully, and fight for the fragile liberty he showed us how to love.
Andrew recently wrote a new conclusion to his book, Righteous Indignation:
'I love my job. I love fighting for what I believe in. I love having fun while doing it. I love reporting stories that the Complex refuses to report. I love fighting back, I love finding allies, and—famously—I enjoy making enemies.
Three years ago, I was mostly a behind-the-scenes guy who linked to stuff on a very popular website. I always wondered what it would be like to enter the public realm to fight for what I believe in. I've lost friends, perhaps dozens. But I've gained hundreds, thousands—who knows?—of allies. At the end of the day, I can look at myself in the mirror, and I sleep very well at night.'
Andrew is at rest, yet the happy warrior lives on, in each of us."
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.
Those who worked closely with Breitbart are commenting about the loss of their colleague.
Dana Loesch is the editor-in-chief of Big Journalism and a contributor for CNN who was mentored by Breitbart.
"Andrew Breitbart was my employer, a dear friend, and my mentor. He was the voice of the new conservative movement, the fiercest defender of the tea party, and an amazing extemporaneous speaker," Loesch wrote in a statement. "There exist people who disagreed with him, even disliked him, but they couldn't dislike him when they got to know Andrew. To know him is to like him, which is why his friends weren't limited to just one ideology. I will miss him."
Joel Pollak, the editor-in-chief of Breibart.com, described his friend and boss as "an extemely kind man and a great friend."
"Andrew would stand up for anybody - left or right. He had friends on both sides. As long as they were willing to play by the same rules, state their biases and respect diversity of opinion," Pollak told ABC News. "He really believed passionately in fairness, and what really made him special was his willingness to fight for it."
Conservative leaders are also expressing the loss of Breitbart in the community.
After giving a speech in Dalton, Ga. this morning, Rick Santorum was asked about Breitbart's death, which had been announced during his speech.
"Obviously prayers go to him and his family and it's a big shock. What a powerful voice," Santorum said. "What a huge loss, in my opinion, for our country and certainly for the conservative movement and the prayers go out to my family. I'm sorry to hear it."
Citizens United President David N. Bossie, issued a statement on Breitbart's passing "with a heavy heart," in which he said, "Andrew was a trailblazer and icon when it came to internet based media. He was truly a one of a kind transformational figure and warrior in the conservative movement and he will be sorely missed."