Dr. Larry Ronan told CNN doctors had ruled out a stroke and Kennedy, 76, would undergo more tests in the coming days to determine why he had a seizure Saturday morning.

The senator was initially treated at Cape Cod Hospital after having "symptoms of a stroke" at his home in Hyannisport, Mass., Saturday. Shortly after his arrival in Cape Cod, he was airlifted to Massachusetts General Hospital, Lt. Bill Rex said.

Kennedy's family said he called from the hospital Saturday and told them he would not be attending a lunch gathering.

He spent the remainder of the day rooting on the Boston Red Sox, surrounded by family members, Ronan said.