A 49-year-old woman was seen because of exertional dyspnea. Two-dimens
ional echocardiography revealed the presence of a large mass in the le
ft atrium. An urgent operation was performed because the tumor suddenl
y stuck in the mitral orifice. The lesion, which occupied the entire l
eft atrium, was resected during cardiopulmonary bypass. Histologic ana
lysis revealed malignant hemangiopericytoma.