Endomyocardial fibrosis (Loeffler's endocarditis) is the main cause of poor outcome in Hyper Eosinophilic Syndrome (HES) and Eosinophilic Leukemia (EL). Reversion of the cardiac damage has been seldom reported, and thrombi can superimpose on infiltrated walls, originating oembolic complications. The tyrosine kynase inhibitor imatinib has been recently employed in patients affected by HES or EL, with impressive results. We have treated with imatinib a young patient affected by Loeffler's endocarditis during EL. Loeffler's endocarditis was studied by transthoracic Doppler echocardiography with and without the contrast agent SonoVue. Cytogenetics, FISH and molecular analysis showed the presence of the FIP1L1/PDGFRA fusion gene, recently detected in a majority of HES patients. Standard echocardiography revealed a large infiltration of the apical region, with apparently pedunculate corpora floating in the LV chamber; after SonoVue injection, a thick endo-myocardial infiltration involving papillary muscles and tendinous chords appeared, which simulated mobile thrombi at standard echography. Treatment with low dose imatinib caused rapid regression of both eosinophilic proliferation and endomyocardiopathy. The fusion gene FIP1L1-PDGFRA was found significantly decreased after a few months of treatment. Using a contrast echocardiographic approach, we demonstrated the non-thrombotic origin of the "in plus" image in our patient and its rapid resolution following imatinib treatment. Imatinib is an excellent candidate for first line treatment of Loeffler's endocarditis, especially when the FIP1L1/PDGFA fusion gene is detected.