This report describes ultrastructural changes in myocardium of 2 patients with dilated cardiomyopathy who had received long term treatment with amiodarone, a highly effective antiarrhythmic agent. Cardiac myocytes and endothelial cells in these two patients contained cytoplasmic inclusions that consisted of electron-dense concentric lamellae and were considered to represent altered lysosomes. These inclusions were morphologically similar to those occurring in other tissues in patients receiving long term therapy with amiodarone.
