Background: In patients with a continuous-flow left ventricular assist device, preimplant predictors of poor physical performance are not well-described. We aimed to identify predictors of inability to walk more than 300 m on 6-minute walk test (6MWT) 6 months after HeartMate 3 implantation. Methods and Results: Using data from the European Registry of Patients Implanted With a Full Magnetically Levitated LVAD, patients with available 6MWT at 6 months after implantation were included (N = 194) and grouped according to 6MWT distance (6MWD) of >300 m (n = 150) or 6MWD of <300 m (n = 44). Patients walking <300 m were older (60 ± 10 vs 52 ± 12 years; P <.001), more often New York Heart Association functional class IV (63% vs 42%; P =.03), and more often had type 2 diabetes (43% vs 17%; P <.001) at implantation. Atrial fibrillation was seen in 57% in those with a 6MWT of <300 m vs 31% in those walking longer (P <.002). Further, hemoglobin and estimated glomerular filtration rate was lower in those walking <300 m (both P <.01). In multivariable regression analysis, independent predictors of a 6MWD of <300 m were: atrial fibrillation (odds ratio [OR], 3.22; 95% confidence interval [CI], 1.12–8.67), older age (OR for 10-year increment, 2.81; 95% CI, 1.55–5.07), New York Heart Association functional class IV (OR, 3.37; 95% CI, 1.27–8.98), and Interagency Registry for Mechanically Assisted Circulatory Support profile 1 or 2 (OR, 6.53; 95% CI, 1.92–22.19). Conclusions: Six months after HeartMate 3 implantation, 77% of patients walked >300 meters in 6 minutes. Apart from age and measures of heart failure severity, atrial fibrillation at implantation is an independent predictor of low 6MWD at 6 months after implantation.