BACKGROUND Hypereosinophilic syndrome (HES) is defined as hypereosinophilia with eosinophil mediated organ damage or dysfunction, provided that other causes of organ damage have been excluded. CASE REPORT An 83-year-old female presented with worsening dyspnea for 3 weeks. She was initially diagnosed with bronchitis and prescribed oral antibiotics along with prednisone taper. However, her dyspnea continued to worsen requiring hospitalization. Physical examination was significant for signs of volume overload. Laboratory investigations were notable for leukocytosis with eosinophilia, elevated BNP (brain natriuretic peptide) and troponin. Electrocardiogram (ECG) showed normal sinus rhythm with non-specific ST-T wave changes. Computed tomography (CT) scan of the chest showed pulmonary edema, bilateral peripheral ground glass opacities, and pleural effusions. Transthoracic echocardiogram (TTE) revealed an ejection fraction (EF) of 45%. She was diagnosed with NSTEMI (non-ST-elevation myocardial infarction) with new onset heart failure; appropriate management was initiated. Left heart catheterization did not show any significant obstructive lesions. Presence of peripheral ground glass opacities on the CT chest scan and eosinophilia raised suspicion for HES. Thorough HES workup was done, all tests came back negative except for elevated serum IgE level. Cardiac biopsy returned positive for eosinophilic myocarditis. Bone marrow biopsy showed 20% eosinophils. Positron emission tomography (PET) scan did not show any hypermetabolic lesions to suggest malignancy. The patient was managed for idiopathic HES with high dose steroids resulting in significant clinical improvement. CONCLUSIONS About 40% of patient with HES manifest cardiac involvement, and one quarter of patients with HES have pulmonary involvement with variable radiologic findings. Steroids remain the mainstay treatment for idiopathic HES.