BOSTON -- Sen. Edward M. Kennedy was undergoing tests at Massachusetts General Hospital Saturday to find out what caused him to have a seizure at the Kennedy compound in Hyannisport.

NewsCenter 5’s medical editor Dr. Timothy Johnson said Kennedy’s seizures could be influenced by previous surgery or family history.

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“There are many possible causes of seizures from what we call idiopathic, meaning we never know the exact cause, to all kinds of secondary causes, ranging from virtually benign to quite serious,” Johnson said.

Kennedy had artery surgery on Oct. 12, 2007, to repair a partially blocked artery in his neck, which Johnson said is meant to help prevent strokes.

“This event today could be related to that surgery,” he said.

"It’s possible that there was a decrease in blood flow that set off the seizure. There also may have been a blood clot that broke away from that area."

Kennedy’s artery problem was found during a routine examination of his back, which was injured in a 1964 airplane crash.

Kennedy’s father Joseph P. Kennedy was severely disabled by a stroke at the age of 73.

“It certainly put him at an increased risk statistically if you have a family history of vascular problems like previous strokes or heart attacks, but it’s impossible to say how much overall it increases risk,” Johnson said.

Kennedy’s office said they wouldn’t know anything more on Kennedy’s condition until more tests are completed.

“They may not find anything definitive by 48 hours, but I’m sure they’ll have some test results by the end of today,” said Johnson.