Sarcopenia, a clinical syndrome primarily associated with reduced muscle mass in the elderly, has a negative impact on quality of life and survival. It can occur secondarily to other diseases such as heart failure (HF), a complex clinical syndrome with high morbidity and mortality. The simultaneous occurrence of these two conditions can worsen the prognosis of their carriers, especially in the most severe cases of HF, as in patients with reduced left ventricular ejection fraction (LVEF). However, due to the heterogeneous diagnostic criteria for sarcopenia, estimates of its prevalence present a wide variation, leading to new criteria having been recently proposed for its diagnosis, emphasizing muscle strength and function rather than skeletal muscle mass. The primary objective of this study is to evaluate the prevalence of sarcopenia and/or dynapenia in individuals with HF with reduced LVEF according to the most recent criteria, and compare the gene and protein expression of those patients with and without sarcopenia. The secondary objectives are to evaluate the association of sarcopenia and/or dynapenia with the risk of clinical events and death, quality of life, cardiorespiratory capacity, ventilatory efficiency, and respiratory muscle strength. The participants will answer questionnaires to evaluate sarcopenia and quality of life, and will undergo the following tests: handgrip strength, gait speed, dual-energy X-ray absorptiometry, respiratory muscle strength, cardiopulmonary exercise, as well as genomic and proteomic analysis, and dosage of N-terminal pro-B-type natriuretic peptide and growth differentiation factor-15. An association between sarcopenia and/or dynapenia with unfavorable clinical evolution is expected to be found, in addition to reduced quality of life, cardiorespiratory capacity, ventilatory efficiency, and respiratory muscle strength.