Eosinophilic myocarditis (EM) is a rare and potentially fatal disease if left untreated. Because the disease can have a delayed presentation and can appear even after 2 years, its underlying causes often remain unknown. We report the case of a 63-year-old man with an atypical clinical presentation of hypersensitive EM and significant coronary artery disease, which was confirmed through coronary angiography. The patient was treated with hydrochlorothiazide (12.5 mg once daily for 2 years) and budesonide/formoterol (160/4.5 µg once daily for 2 years). Amoxicillin/clavulanic acid (1000/200 mg three times daily for 2 days) and azithromycin (500 mg once daily for 2 days) were used to treat pneumonia, while ibuprofen (600 mg three times daily for 2 days) was used to treat pericarditis. Extremely high levels of eosinophils led to clinical suspicion of non-acute coronary syndrome as the cause of chest pain and myocardial necrosis. In addition, early pulse doses of methylprednisolone (500 mg intravenously once daily) were administered. Complete clinical recovery and a fast decrease in eosinophils and troponin levels were observed after a few hours on the same day. No signs of recurrent myocarditis were noticed after 3 days of administering the same pulse doses of methylprednisolone, which was then replaced by oral methylprednisolone administered for the next 2 months (step-down regimen, starting from 64 mg/day). Despite causality assessment being difficult, prompt therapy must be given as soon as possible to prevent fatal outcomes. Delayed corticosteroid treatment, which is necessary regardless of the underlying cause, can result in heart failure and death.