We hypothesized that older age, female sex, more comorbidities, β-blocker usage, lower heart rate, poorer cardiac function (as measured by higher B-natriuretic peptide, BNP), anemia, higher IL-6, greater daytime sleepiness, more depression, and lower social support would explain fatigue 6–8 months post-MI among elderly adults. Here, NPPB is linked to anemia (phenotype).