Background: The timed up and go test (TUGT) is a short-duration functional test frequently used in rehabilitation settings as a measure of balance and mobility. Reliability and validity for patients with chronic heart failure (CHF) has yet to be determined. This prospective cohort study aimed to determine test-retest reliability of the TUGT in patients with CHF, relationships between the TUGT and other variables, including functional tests, and predictors of the TUGT. Methods and Results: This was a secondary analysis of data collected in a multicenter randomized controlled trial of exercise training in recently hospitalized patients with heart failure (EJECTION-HF). The TUGT was conducted twice at baseline to determine reliability. Assessments were compared with 6-minute walk distance (6MWD), 10-m walk test time, and other clinical variables. Intraclass correlation coefficient (ICC) was used to determine test-retest reliability and correlations for relationships with other variables. A multiple regression was used to identify predictors of the TUGT. In 278 participants (mean age 62 years), the TUGT demonstrated excellent within-day test-retest reliability (ICC 0.93). A shorter (better) TUGT time was associated with longer 6MWD (r 5 0.81; P ! .001) and shorter 10-m walk test time (rs 5 0.80; P ! .001). Best predictors of the TUGT were 6MWD and age, which accounted for 66% of the variance. Conclusions: The TUGT appears to be a reliable and valid functional measurement in patients with CHF.