A catecholamine-induced dilated cardiomyopathy is reported in a patient with multiple endocrine neoplasia, type 3. A histologic and ultrastructural study has been undertaken in cardiac biopsy samples, together with determination of myocardial Ca++ and cellular membrane fatty acids. Contraction band necrosis of cardiocytes with supercontraction of sarcomeres progressing to myofibrolysis and increased levels of myocardial Ca++ have been found as morphologic and biochemical abnormalities, respectively. No lipoperoxidation of cellular membranes or an alpha-adrenergic mediated reduction of coronary supply could be recognized in the study. We indicate a receptor-mediated intracellular Ca++ overload as the main abnormality responsible for myocardial impairment.