We have reported the clinical and biochemical findings in juvenile visceral steatosis (jvs) mice with systemic carnitine deficiency. This paper is the first report about cardiomyopathy in jvs mice. Adult jvs mice (at the age of 2-3 months) show cardiac hypertrophy which is caused by enlargement of the cardiac muscle cell associated with increases of non-collagen protein and DNA content. Carnitine administration (2 mg/head, twice a day, from 1 month of age) significantly suppresses the cardiac hypertrophy, showing that carnitine deficiency plays an important role in the development of the cardiac hypertrophy. The discovery of cardiac hypertrophy in carnitine-deficient jvs mice will lead to clarification of the pathophysiology of cardiomyopathy in systemic carnitine deficiency in human beings.