In the multiplex cytokine assay, the patient with myopericarditis after COVID-19 vaccination revealed a marked increase of four cytokines and chemokines, IL-18, IL-27, CXCL9, and CXCL10, over vaccinated controls who experienced no cardiac complications, suggesting that cardiac injury could be mediated by those soluble factors. This evidence concerns the gene CXCL9 and COVID-19.