David Brock, the founder of left-wing news outlet Media Matters for America and a longtime friend of the Clintons, suffered a heart attack on Tuesday.
Brock was a conservative journalist before becoming a major influential figure for many liberal groups, the Washington Examiner reports.
A press release was issued on Wednesday stating that Brock had a heart attack.
"David Brock suffered a heart attack while working in the Washington, D.C. office early Tuesday," the statement said.
"He was quickly transported to a local hospital, received prompt medical treatment, and we are looking forward to a swift recovery," the statement continued.
Brock became one of the Clintons' top political associates and has been involved in many liberal political groups, including Media Matters.