A case of hypereosinophilic syndrome showed clinical and hemodynamic signs of Löffler's endomyocardiopathy. The case is peculiar because of the young age, the early diagnosis, the lack of clinical and hemodynamic signs of heart failure. Some peculiarities: an apical diastolic murmur and a diastolic pulmonary capillaries/left ventricle pressure gradient recalled the picture of mitral stenosis, but the echocardiographic pattern of mitral valve was normal; a sistolic aortic and pulmonary subvalvular gradient, with an increase in ventricular wall thickness, was present. Echocardiography, systolic time intervals, and maxdp/dt and Vmax showed a very good left ventricular function. The patient is still in good compensation, with unchanged clinical pattern and eosinophilia, despite the therapeutical attempt with corticosteroids and antiallergic drugs, after one year from the diagnosis. The pathogenetic hypothesis of this cardiac and hematologic disorder are discussed.