Background Frailty is prevalent in older adults with heart failure and is associated with poor outcomes; however, there remains uncertainty on how to measure frailty in clinical practice. Methods and Results A multicentric prospective cohort study was assembled at 4 heart failure clinics to compare the prognostic value of 3 physical frailty scales in ambulatory patients with heart failure. Outcomes were all-cause death or hospitalization and health-related quality of life using the 36-Item Short Form survey questionnaire (SF-36) at 3 months. Multivariable regression was adjusted for age, sex, Meta-Analysis Global Group in Chronic Heart Failure score, and baseline SF-36 score. The cohort included 215 patients (mean age 77.6 years). All 3 frailty scales were independently associated with death or hospitalization at 3 months; the adjusted odds ratios standardized per 1 SD worsening of the Short Physical Performance Battery; Fried, and strength, assistance with walking, rising from a chair, climbing stairs, and falls scales were 1.67 (95% CI, 1.09-2.55), 1.60 (95% CI, 1.04-2.46), and 1.55 (95% CI, 1.03-2.35), respectively, with C statistics of 0.77 to 0.78. All 3 frailty scales were independently associated with worsening SF-36 scores, especially the Short Physical Performance Battery, for which 1 SD worsening of frailty translated to a decrement of -5.86 (-8.55 to -3.17) and -5.51 (-7.82 to -3.21) points in the Physical Component Score and Mental Component Score. Conclusions All 3 physical frailty scales were associated with death, hospitalization, and reduced health-related quality of life in ambulatory patients with heart failure. Questionnaire or performance-based physical frailty scales can be used to offer prognostic value and a therapeutic target in this vulnerable population. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT03887351.