['In chronic heart failure (CHF), low body mass as a reflection of low muscle mass has been associated with poor outcome. Urinary creatinine excretion rate (CER) is an established marker of muscle mass, but has not been investigated in CHF. This study aims to evaluate urinary CER as a marker of muscle mass in patients with CHF and establish the relationship with clinical outcome.', 'In 120 patients with CHF, we evaluated CER as determined by mean creatinine excretion rate in two consecutive 24-h urine collections. We evaluated the relationship between CER and clinical variables using linear regression. Finally, we evaluated the association between CER and clinical outcome. Mean age was 59 ± 12 years, and 80% were male. Mean CER was 1,383 mg/day (range 412-2,930). Independent predictors of CER were body surface area (BSA) (β = 0.404, P < 0.001), gender (β = -0.180, P = 0.029), log N terminal pro-brain natriuretic peptide (NTproBNP) (β = -0.172, P = 0.048) and age (β = -0.168, P = 0.035). During three years of follow-up, 33 patients (28%) developed a clinical endpoint, defined as the first occurrence of either all-cause death, heart transplantation, myocardial infarction, or hospitalization for heart failure during three years of follow-up. In Cox regression analyses, log CER was associated with the occurrence of the clinical endpoint independent of age, gender, BSA, glomerular filtration rate and urinary albumin excretion, [hazard ratio 7.67 (1.82-32.3) per log decrease], but not independent of NTproBNP [hazard ratio 3.66 (0.79-17.0), P = 0.098].'] Is creatinine excretion rate , a marker of muscle mass , related to clinical outcome in patients with chronic systolic heart failure?