Loeffler endocarditis is a rare heart disorder, characterized by endomyocardial involvement of heart ventricles in patients with persistent eosinophilia. The pathology is leading to restrictive cardiomyopathy, resistant heart failure and negative prognosis. Cardiac imaging and eosinophil count monitoring provide the clues to the diagnosis. We present a case of a 32-year old female patient with abrupt onset of right-sided heart failure. The patient was diagnosed with myocardial infarction without coronary artery obstruction 2 years before the admission and was in stable condition with mid-range ejection fraction during follow-up. Her status deteriorated several days before admission with increasing dyspnoea and swollen legs. The echocardiography showed severe left ventricular systolic dysfunction, normal right ventricular systolic function with restrictive filling pattern due to massive thrombosis of its cavity, proved by cardiac computed tomography. The eosinophils count was elevated, the diagnosis of Loeffler endocarditis was established. Corticosteroids were prescribed with conventional therapy of heart failure and anticoagulation. The right ventricular mass resolved gradually during 3-5 month and right ventricular filling normalized with concomitant improvement of patient’s clinical status. The patient was on tapering doses of prednisolone for 6 months and on maintaining dose for 2 years. Two and half years after Loeffler endocarditis the patient deceased suddenly with signs of acute dyspnoea. An autopsy showed mild right-sided endocardial fibrosis, extensive interstitial left ventricular fibrosis consistent with a diagnosis of chronic myocarditis of unspecified aetiology and bronchospasm with eosinophilic material inside bronchi.