Eosinophilic endomyocarditis is extremely rare in paediatrics. This case report aims to present the sequential changes from thrombotic to fibrotic stages of the cardiac involvement in a child with hypereosinophilic syndrome. Endomyocardial fibrosis progressively aggravated the severity of the mitral regurgitation. Bioprosthetic valve replacement was finally performed without recurrence of cardiac complications despite a late relapse of the underlying disease.