A malignant mesenchymoma is a rare soft tissue neoplasm that show at least two types of malignant mesenchymal differentiation, in addition to poorly differentiated fibrosarcomatous elements. They grow rapidly, recur frequently, and can be found in a wide variety of location, with most occurring in the extremities. A primary malignant mesenchymoma of the heart is extremely rare, with only 20 cases having been reported worldwide in the English literature up to 2002. We experienced a case of primary cardiac malignant mesenchymoma in a 59 year old female patient, who was admitted due to exertional dyspnea. This case is reported, with a review of the relevant literature.