The authors report a case of a 35 year old man with of congestive cardiac failure. Echocardiography showed diffuse hypokinetic wall motion with moderate parietal hypertrophy without dilatation. Post-mortem examination showed intramyocardial deposits of light chains identical to those observed in "in vivo" renal and liver biopsies. This rarely described disease has a poor prognosis. It is characterised by polyvisceral infiltrations of light chain monoclonal immunoglobulins. Renal disease is usually the main problem progressing rapidly to renal failure. Of the extra renal localisations, cardiac involvement would appear to be common and preoccupying in itself. Monoclonal plasmocytic proliferation is observed in all cases, the majority but not all being malignant (myeloma). The incidence of this condition is probably underestimated and may pass undetected if immunofluorescent techniques are not used. Myelomatous light chain cardiac disease could therefore be more common than amyloidosis with which it presents a number of common features.