I've been experiencing some cognitive issues since my heart valve replacement in Oct. 2012.  Naturally I was told 8 to 12 weeks that there may be some impairment. Wow, some? I'd go into a room, forget why I went in, walk out and remember, go back in and forget. I might understand some of this if I were more elderly and exhibited signs pre-op, but I'm 46 and had no issues prior. But it still goes on. The symptoms got better over the next few months (I was actively using my brain, challenging it - interacting with folks). I noticed some slip ups with speech (nothing major, just one or two words would be difficult to pronunciate. I'm in my Masters program currently and can do my studies ok. I've noticed some issues with my writing though. It seems much more disjointed or scattered. About 10 months post-op I noticed a feeling of numbness, almost like being in a fog. It felt like someone had unplugged my brain. It's real folks. It's not easy to deal with and very hard to explain to someone when it is happening. It can be debilitating to say the least.
I had no health issues (other than the occasional elevated BP - nothing alarming) other than the discovery (purely by accident) of a undiagnosed heart valve defect (which was discovered at age 44). The valve began to deteriorate and was replaced before any permanent damage was done.
So to my point, it is something to consider. If you have a loved one who is experiencing this (or you notice the change in behavior - walking around dazed and confused), have it checked out. There is not enough research at this point and if people continue to sweep the condition under the rug and attribute it to the aging process, nothing will change.
I hope this is able to give some relief to someone who is struggling with this (or a family member who may be).
Yes the alternative of not doing the surgery has a much more grim outlook, but there is no reason for someone to go through the recovery process only to have this battle to contend with as well.