This is a report of one case of L5ffler`s eosinophilic endocarditis associated with mitral insufficiency and LV thrombi treated surgically at the department of Thoracic and Cardiovascular Surgery, Hanyang University Hospital. This patient was a 42 year old female and she has complains of dyspnea, palpitation, orthopnea and generalized edema. Above symptoms has been going for 4 months and NYHA classification was IV. On examination, blood eosinophil was 45 to 50% [WBC-9800 ]. MI and LV thrombi were confirmed by LV ventriculography and echocardiography. Pulmonary congestion and congestive cardiac failure were diagnosis by X-Ray examination, EKG finding and clinical feature and others there were no organic functional disturbance. Mitral valve replacement was performed with Ionescu-Shiley pericardial valve [29mm] replacement. Adjust thumb sized grayish brown colored two thrombi were excluded, lodged in the apex and septal endocardium of LV. Endocardial fibrosis was reliably confirmed under the gross pathology in the heart. The patient had smooth postoperative course and there were no operative complication. [KTCS 1983;4:526-532]