Hereditary hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease, but the genetic defects are still unclear in many cases. Reduced myocardial long-chain fatty acid (LCFA) uptake has been demonstrated in patients with some types of HCM. In addition, a possible relationship between a shift ofmyocardial substrate utilization and cardiac hypertrophy has been suggested by experimental studies. Myocardial uptake of LCFAs occurs via a specific transporter, which is homologous with human CD36. CD36 deficiency has also been reported in some individuals, and is transmitted as an autosomal dominant trait like HCM. In this study, we analyzed CD36 in 47 patients with HCM [29 with asymmetric septal hypertrophy (ASH) and 18 without ASH], 11 patients with dilated cardiomyopathy (DCM), and 26 patients with pressure-overload cardiac hypertrophy. Eleven patients (37.9%) who had HCM with ASH, one (9.1%) with DCM, and two (7.7%) with pressure-overload hypertrophy showed CD36 deficiency, while none of the HCM patients without ASH had CD36 deficiency. One patient who had HCM with ASH and CD36 deficiency showed no myocardial LCFA uptake, although myocardial perfusion was normal. Reduced myocardial LCFA uptake despite normal myocardial perfusion was demonstrated in the other HCM patients with ASH and CD36 deficiency. Based on the high prevalence of CD36 deficiency in HCM patients with ASH, we hypothesize that this deficiency might be one etiology of hereditary HCM.