A 63-year-old man with anterior chest oppression was diagnosed as an acute myocardial infarction. The two-dimensional echocardiogram revealed a mass which bulged into the left ventricular cavity. Subsequently, the computed tomographic findings of the mass lesion demonstrated the attenuation values of -49 Hounsfield units, which corresponded to that of fatty tissues. From these findings the left ventricular lipoma was highly suspected. The tumor existed at the base of the anterior papillary muscle. It was successfully resected and mitral valve replacement was performed concomitantly. The tumor was yellowish and sized by 25 X 20 mm. On histological examination of the specimen, the tumor was composed of mature fatty cells. CT scanning was very useful for the preoperative evaluation of lipoma.