Background Patients on long-term hemodialysis become deficient in carnitine and are frequently treated with carnitine supplementation to offset their renal anemia, lipid abnormality and cardiac dysfunction. The therapeutic value of carnitine supplementation on left ventricular hypertrophy (LVH) in patients with normal cardiac systolic function remains uncertain. Methods and Results The cardiac morphology and function of 10 patients given 10 mg/kg of L-carnitine orally, immediately after hemodialysis sessions 3 times per week for a 12-month period were compared with 10 untreated control patients. Using echocardiography, left ventricular fractional shortening (LVFS) and left ventricular mass index (LVMI) were measured before and after the study period. As a result, amounts of serum-free carnitine increased from 28.4±4.7 to 58.5±12.1 μmol/L. The LVMI decreased significantly from 151.8±21.2 to 134.0±16.0 g/m² in treated patients (p<0.01), yet the LVMI in untreated control patients did not change significantly (ie, from 153.3±28.2 to 167.1±43.1 g/m²). However, LVFS values remained unchanged in both groups. Although L-carnitine promoted a 31% reduction in erythropoietin requirements, hematocrit and blood pressure did not change during the study period. Conclusions Supplementation with L-carnitine induced regression of LVH in patients on hemodialysis, even for those with normal systolic function. (Circ J 2008; 72: 926 - 931)