A case of a 3 and a half years old girl with severe congestive heart failure, and typical picture of dilated cardiomyopathy is presented. The serum level of carnitine (17.2 micromoles/l, versus 44.1 +/- 12.2 micromoles/l, normal value for age) and the histologic and biochemical evaluation of quadriceps muscle tissue confirmed the diagnosis of primary deficit of carnitine. L-carnitine (2 gr. three times a day p.o.) was added to anti-congestive therapy. After 8 weeks of therapy, the general and cardiocirculatory conditions are much improved. The physiopathology of dilated cardiomyopathy due to deficit of carnitine are discussed. An early diagnosis, and an early substitutive therapy with L-carnitine dramatically improve the outcome of the disease.