The exact mechanism by which clozapine causes cardiac side effects is unclear. Kilian et al. proposed an IgE-mediated hypersensitivity (type 1 allergic reaction) or type 3 allergic reaction (serum sickness) as the mechanism of clozapine-induced myocarditis based on findings of peripheral eosinophilia and eosinophilic inclusions on cardiac biopsy [8]. Here, IGHE is linked to Increased total eosinophil count.