This is a prospective cohort study aiming to construct a prediction model for postoperative cognitive dysfunction (POCD) in elderly cardiac patients. We plan to enroll elderly patients aged ≥65 years undergoing cardiac surgery. Peripheral blood samples and functional magnetic resonance imaging (fMRI) data will be collected at baseline and key time points post-surgery. The primary objectives are to identify novel peripheral blood protein biomarkers for POCD, explore the correlation between fMRI characteristics and POCD, and establish a reliable early prediction model to improve perioperative management and reduce the incidence of POCD in elderly cardiac surgical patients.