My dad had a heart attack a while back but after it hes been feelining fine now his brains blury like hes not as sharp. What could that be?

Circulation. Heart attack means circulation is compromised. If that affects the heart that means most of the circulation is compromised already.Which includes the brain also. So controlling blood pressure, cholesterol, blood sugar and weight contributes to the circulation integrity. Make sure to have a work up done to check brain circulation including carotid ultrasound and brain mri.
A stroke. Sometimes a heart attack is accompanied by a stroke -- and this could be what happened to your dad -- take him to a doctor for evaluation of a possible stroke old or new?