Tuesday, 11 September 2012, 09.30 -10.30 Objective: Intravenous leiomyomatosis is a very rare growth pattern variant of leiomyoma in which nodular masses of tumor grow within venous channels. Occasionally the tumor can extend to vena cava and the right heart. Method: We present a case of a 45-year-old woman, who was admitted in the emergency room with rapidly evolving exertional dyspnea. Cardiac ultrasonography revealed a "big mass in the right chambers". She was submitted to a right atriotomy with resection of part of the tumor, which was sent for intraoperative consultation. Results: Grossly, the tumor was polypoid, firm, with a smooth surface. The frozen section showed a lesion composed of tortuous vessels and in some areas a fibrillar eosinophil extracellular matrix and others with spindle cells. No significant atypic or pleomorphic cells, mitosis or necrosis were observed. The diagnosis was deferred for definitive paraffin sections. In the definitive H&E and with immunohistochemical stains, the case was diagnosed as an intravenous leiomyomatosis, and the diagnosis was confirmed in the hysterectomy specimen. Conclusion: Intravenous leiomyomatosis with cardiac involvement is an extremely rare condition. Clinical information is essential for the correct diagnosis in frozen section.