We conducted postmortem examination of a patient with primary macroglobulinemia whose heart failure and anemia had been controlled with a total of 181 double filtration piasmaphereses (DFPP) over a 7 year period. The patient was a 56-year-old male with primary macroglobulinemia and multiorgan failure, but chemotherapy was difficult to perform because of granulocytopenia. The cause of death was congestive heart failure. On postmortem examination, the heart was markedly enlarged, weighing 660g and there was no apparent evidence of deposition of a uniform structural substance in the myocardium. Mitral and aortic valvular annuluses were enlarged, presumably due to dilatation of the left ventricle. The main cause of death in this patient was suggested to be congestive heart failure caused by impaired contractility of the left ventricle and mitral and aortic regurgitation due to dilatation of the valvular annuluses.We suggest that DFPP is useful for treating patients with primary macroglobulinemia having increased preload and myocardial iscemia, due to hyperviscosity syndrome, as in our patient because this procedure can selectively eliminate IgM.