Methods and results: We retrospectively analysed 212 HF patients (73 � 13 years old; 41% females) who underwent dual-energy X-ray absorptiometry (DXA), abdominal CT imaging, and amino acid profiling, of whom 186 had complete sarcopenia assessment. Sarcopenia was diagnosed based on the Asian Working Group for Sarcopenia 2019 criteria using DXA-measured appendicular skeletal muscle mass index and grip strength, with severe sarcopenia additionally requiring low Short Physical Performance Battery scores. CT-measured skeletal muscle area index (SMI) at the lumbar vertebral level combined with grip strength showed high diagnostic accuracy for sarcopenia [area under the receiver operating characteristic curve (AUC): 0.96 for males, 0.88 for females], with optimal cut-off values of 54 cm2/m2 for males and 40 cm2/m2 for females. SMI was similarly reduced in non-severe and severe sarcopenia patients, whereas mean muscle attenuation (MMA), an index of intramuscular lipid infiltration, was decreased exclusively in patients with severe sarcopenia. In multivariable analysis adjusted for age, sex, HF functional class and diabetes, decreased MMA remained the only CT-measured index significantly associated with low physical performance. MMA showed higher predictive value than SMI for severe sarcopenia in males (AUC 0.81 vs. 0.54, P = 0.039). Several amino acids (leucine, β-alanine and 3-methylhistidine) and the Fischer ratio were significantly associated with MMA, independent of SMI and established MMA determinants including sex, age, and body mass index.