Bill Fraser was taken to the Dr. Everett Chalmers Hospital in Fredericton by ambulance mid-afternoon after complaining of chest pains.
The 43-year-old legislature member for the riding of Miramichi-Bay du Vin was walking across the parking lot from the Opposition office to the legislature when he began feeling ill.
He was sitting in his vehicle near the legislature when the ambulance was called.
A statement from the Opposition says Fraser remains in the cardiac unit of the hospital and is awaiting more test results.
Fraser was first elected in September 2006.