Background: Frailty among cardiac rehabilitation (CR) participants is associated with worse health outcomes. However, no literature synthesis has quantified the relationship between frailty and CR outcomes., Purpose: Examine frailty prevalence at CR admission, frailty changes during CR, and if frailty is associated with adverse outcomes following CR., Methods: We searched CINAHL, EMBASE, and MEDLINE for studies published from 2000-2023. Eligible studies included a validated frailty measure, published in English. Two reviewers independently screened articles and abstracted data. Outcome measures included admission frailty prevalence, frailty and physical function changes, and post-CR hospitalization and mortality., Results: Observational and randomized trials were meta-analyzed separately using inverse variance random-effects models. 34 peer reviewed articles (26 observational, 8 randomized trials; 19,360 participants) were included. Admission frailty prevalence was 46% [95% CI 29%, 62%] and 40% [95% CI 28%, 52%] as measured by Frailty Index and Kihon Checklist (14 studies) and Frailty Phenotype (11 studies), respectively. Frailty improved following CR participation (SMD; 0.68, 95% CI 0.37, 0.99; P<.0001; 6 studies). Observational studies meta-analysis revealed higher admission frailty increased participants' risk of all-cause mortality (Hazard ratio: 9.24, 95% CI 2.93, 29.16; P=.0001; 4 studies). Frailer participants at admission had worse physical health outcomes, but improved over the course of CR., Conclusions: High variability in frailty tools and CR designs was observed, and randomized controlled trials contributions were limited. The prevalence of frailty is high in CR and is associated with greater mortality risk; however, CR improves frailty and physical health outcomes., (© The Author(s) 2024. Published by Oxford University Press on behalf of the European Society of Cardiology.)