An 86 year old female presented to the emergency department with a one week history of leg swelling and recent weight gain. An echocardiogram revealed an 8.7 x 5 cm mass of the right atrium that appeared to be adherent to the atrial wall and filled over 90% of the volume of the right atrial chamber. The patient expired approximately one month later, and an autopsy limited to the heart and pericardial sac was requested. The autopsy confirmed the presence of a 9 cm mass involving the right atrium and completely encasing the right coronary artery. Microscopically the tumor was composed of sheets of plasma cells. Immunohisto-chemical studies showed that the cells were kappa light chain restricted, strongly positive for LCA and CD79a, and negative for CD138 and CD20. Given the gross and microscopic findings, the lesion was diagnosed as an extramedullary plasmacytoma of the heart.