Introduction Hypereosinophilic syndrome (HES) is a myeloproliferative disorder characterized by persistent eosinophilia that is associated with damage to multiple organs. Case Presentation Herein, we describe a case of left ventricular (LV) Löffler endocarditis on top of idiopathic HES leading to inflow and outflow obstruction. The posterior mitral leaflet was involved in the fibrotic process leading to severe mitral valve regurgitation. There was a mural thrombus in the left ventricle, which resulted in thrombo-embolic complications in the form of lower limb ischaemia. The patient was treated with high-dose corticosteroids and anticoagulants with significant improvement of his cardiac condition. Discussion In patients with persistent hypereosinophilia, thorough workup is recommended to identify any possible primary cause and detect associated end-organ damage. Treatment should be started as early as possible after establishing the diagnosis to reduce morbidity and prevent complications. Corticosteroids are the first-line therapy that usually cause a rapid reduction in the level of the eosinophilia and must be started promptly if cardiac involvement is present to attain rapid reduction in the eosinophil level and reverse the cardiac damage.