We present the fourth case report of an histiocytoid hemangioma of the heart, which was found incidentally, as in the other three reported cases, in a 50 year old man during surgery for congenital heart disease. A polypoid sessile reddish tumor with a smooth surface, which measured 2 cm in diameter, was found in the right atrium. No necrosis nor cystic areas were seen. Histologic evaluation revealed a proliferation of histiocytoid or epithelioid cells, whose arrangement varied a great deal within the infiltrate. Sometimes, the cells were isolated but in most places they were arranged in sheets or nests surrounded by connective tissue. Some of these nests were compact whereas in others a lumen formation, frequently occupied by erythrocytes, could be appreciated. A striking feature was the presence of vacuolated tumor cells sometimes assuming a signet-ring configuration. Some large vascular spaces were lined by histiocytoid or epithelioid endothelial cells, many of which protruded into the lumen. Multinucleated tumor cells were occasionally observed. Mitoses were rare (up to 1/10 HPF) and scattered inflammatory cells such as lymphocytes, macrophages, neutrophils and eosinophils were seen. Histologic appearance of our patient's tumor is identical to the histiocytoid hemangioma of Rosai et al., which is an ubiquitous endothelial benign neoplasm.