One of the best kept secrets about heart by pass surgery is the high incidence of strokes after the surgery.
My wife's best friend had a severe stroke 6 years ago Christmas Eve. The by pass was successful, and she all most died from the stroke.
Six years later, she is still unable to talk except for a few words and still has problems walking and getting up. In fact she fell and broke her hip this past summer.
What is amazing is she can still play incredible bridge with a system we came up with and balances their checkbook to the penny. Her great mind is there, she just can't verbalize her thoughts and comments.