Idiopathic hypereosinophilic syndrome is a rare condition characterized by persistent severe eosinophilia and organ damage without any apparent cause.A 20-year-old male patient with no significant medical history was admitted to the Emergency Department with retrosternal chest pain, fatigue and asthenia. EKG showed ST elevation I, II, III, aVF, V4-V6 and blood tests showed elevated troponin levels. An echocardiogram was performed revealing severe global left ventricular systolic dysfunction. Further evaluations included cardiac magnetic resonance imaging and endomyocardial biopsy, confirming the diagnosis of eosinophilic myocarditis. The patient was started on systemic corticosteroid therapy, resulting in clinical improvement. The patient was discharged after 12 days of hospitalization, following a recovery of biventricular function and he was told to continue oral corticosteroid therapy at home. Further investigation ruled out other causes of hypereosinophilic syndromes, therefore the diagnosis of idiopathic hypereosinophilic syndrome was assumed. Despite the attempt to reduce corticosteroid therapy, the eosinophil count became elevated again, so the dosage was increased and associated with azathioprine with subsequent favorable analytical evolution.This case highlights the challenges in diagnosing and managing idiopathic hypereosinophilic syndrome and emphasizes the importance of prompt treatment initiation to prevent complications.