RESUMEN
A 19-year-old male presented with fever, substernal pain, dyspnea, and distended neck veins. Diagnostic investigations, such as echocardiography and magnetic resonance imaging, provided evidence of a large mass within the pericardial sac, attached by a broad base to the parietal pericardium and lying along the right ventricular free wall. A partial pericardiectomy was performed to relieve the patient's symptoms, and histologic examination of a biopsy specimen showed features of a malignant, spindle cell, mesenchymal neoplasm. The patient underwent surgical treatment during which the tumor was found to infiltrate the anterior surface of the right ventricle. Histologically, the tumor was identified as a high-grade fibrosarcoma, and additional chemotherapy was given.