Loefler endocarditis is a potential fatal adverse event of hypereosinophilic syndrome. We report a case of a 5-year-old girl diagnosed with peripheral hypereosinophilia refractory to corticosteroid therapy who developed eosinophilia-related endocarditis. Echocardiography revealed infiltration of the left ventricular free wall and the posterior mitral leaflet causing moderate mitral regurgitation. Genetic tests failed to recognize FIPiLi-PDGRFA genotype; however imatinib, a tyrosine kinase inhibitor was initiated. After a 4-week period of treatment there was a complete resolution of eosinophilia and a complete recovery of cardiac manifestation. This case highlights the introduction of imatinib for the treatment of hypereosinophilic syndrome refractory to corticosteroid therapy even in the absence of FIPiLi-PDGRFA genotype in pediatric patients.