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The discovery of eosinophilia above 1.5 G/L should not be considered innocuous, with monitoring required in the search for etiologies and potential secondary organ damage. Among the latter, cardiac involvement, which can be indolent, is the most concerning possibility, requiring systematic investigation by ultrasound and magnetic resonance imaging. There are many potential etiologies, the vast majority of which are reactive and cortico-sensitive. In much rarer cases, the condition may be of clonal origin and associated with a hematological malignancy (chronic or myeloid), which may be responsive to tyrosine kinase inhibitors.