Abstract Background Sarcopenia, the loss of skeletal muscle mass and function, is recognized as a negative prognostic factor in heart failure patients. Current guidelines, such as those by the Asian Working Group for Sarcopenia (AWGS), emphasize quantifying muscle mass using methods like bioelectrical impedance analysis or dual-energy X-ray absorptiometry, known for their precision. In contrast, the Sarcopenia Definitions and Outcomes Consortium (SDOC) focuses on functional parameters. However, its applicability and effectiveness as a prognostic indicator in heart failure remain uncertain. Purpose To determine the prognostic utility of sarcopenia determined by the SDOC diagnostic criteria in predicting all-cause mortality among older patients with heart failure, and to compare its prognostic predictability with that of the AWGS 2019 diagnostic algorithms. Methods This was a post-hoc analysis of the FRAGILE-HF study, a prospective, multicenter, observational study involving patients aged ≥65 years hospitalized for heart failure. Sarcopenia was diagnosed according to two definitions: AWGS 2019 guidelines criteria and the SDOC criteria, which diagnose sarcopenia based only on grip strength and gait speed. With SDOC criteria, patients were divided into three groups: sarcopenia (low grip strength and decreased gait speed), pre-sarcopenia (low grip strength or decreased gait speed), and non-sarcopenia (normal grip strength and normal gait speed) groups. Two logistic models for the primary outcome were constructed by adding the information on pre-sarcopenia and sarcopenia defined by AWGS 2019 and SDOC to the MAGGIC-HF risk score + log BNP, and prognostic predictability was compared by receiver operating characteristic curve areas under the curve (ROC-AUC) and net-reclassification improvement (NRI) between three models. The primary outcome was 2-year mortality. Results Of 1282 study patients, pre-sarcopenia and sarcopenia were diagnosed in 357 and 786 individuals, respectively, according to SDOC criteria. The Kaplan-Meier analysis revealed a significant stepwise association between the sarcopenic status and the primary outcome. The adjusted Cox proportional hazards analysis indicated a significant stepwise association between sarcopenic status and mortality risk (pre-sarcopenia, hazard ratio [HR]: 1.22, 95% confidence interval [CI]: 0.66–2.28, P= 0.525; sarcopenia, HR: 1.89, 95% CI: 1.08–3.34, P= 0.027). No significant difference was observed in the prognostic capabilities between the two models adding sarcopenia defined by SDOC and AWGS 2019 diagnostic criteria to the model incorporating the MAGGIC-HF risk score + log BNP (NRI: -0.009, 95% CI: -0.193–0.174, P=0.920, with ROC-AUC of 0.697 for SDOC and 0.703 for AWGS 2019, P=0.675, respectively). Conclusion Diagnosing sarcopenia with the SDOC criteria, which does not include muscle mass, provides incremental prognostic information as same as that defined by AWGS 2019 criteria.Figure