Objective To determine whether biomarkers of health such as serum levels of free triiodothyronine (fT3), total triiodothyronine (TT3), N-terminal pro-B-type natriuretic peptide (NT-proBNP), and high-sensitivity C-reactive protein (hsCRP) impact the cognitive functioning of coronary artery disease (CAD) patients. Method About 278 patients were evaluated for socio-demographic and clinical risk factors as well as fT3, TT3, NT-proBNP, and hsCRP serum levels. Cognitive functioning measures included the Mini-Mental State Examination, Digit Span Test, Digit Symbol Substitution Test (DSST), and Trail Making Test A (TMTA). Depressive symptoms were assessed with the Hospital Anxiety and Depression Scale. Results Lower fT3 concentrations were associated with longer completion time of the DSST and TMTA. Elevated levels of NT-proBNP were also associated with inferior performance on TMTA independently of socio-demographic characteristics, clinical risk factors, and depression symptoms. Conclusions Lower fT3 concentrations and higher levels of NT-proBNP were associated with worse cognitive functioning in CAD patients.