Abstract: Objective:To investigate the pathological diagnosis and pathological characteristics of primary heart malignant fibrous histiocytoma.Methods:One case of primary cardiac malignant fibrous histiocytoma was observed by light microscopy and immunohistochemistry,and the literature was reviewed.Results:The tumor which was divided into three sub-leaves was located on the posterior wall of the left atrium,with a maximal diameter of 2.0 to 4.5 cm;microscopically,the tumor cells were mostly in the shape of spindle,showing fascicular arrangement;myxo-matrix,rich blood vessels and interstitial chronic inflammatory cell infiltration could be observed.Immunophenotype showed tumor cells of vimentin strongly positive,CD68,Ki-67 (>50%),SMA (focal) and S-100 protein positive,CD34 and desmin negative.Conclusions:Cardiac malignant fibrous histiocytoma is frequently misdiagnosed as atrial myxoma;correct diagnosis should be based on pathological examination and immunohistochemistry.This tumor is highly malignant,easy to relapse and has a poor prognosis.