Ans. C. Cognitive dysfunction* The history of cardiac surgery 2 days prior followed by behavioral changes is suggestive of delirium. The questions here is stressing on "disturbances of memory'' which can be seen in delirium, however, are usually restricted to short term memory loss.* The other important features such as clouding of consciousness and attention impairment has not been provided.* Nonetheless, the most likely diagnosis appears to be delirium. As delirium has prominent cognitive dysfunction, that is the correct answer.* Alzheimer disease does not have such sudden onset.