OBJECTIVES: The objective of this study was to assess the prognostic significance of exercise capacity in patients with ischemic left ventricular (LV) dysfunction eligible for coronary artery bypass graft surgery (CABG). BACKGROUND: Poor exercise capacity is associated with mortality, but it is not known how this influences the benefits and risks of CABG compared with medical therapy. METHODS: In an exploratory analysis, physical activity was assessed by questionnaire and 6-min walk test in 1,212 patients before randomization to CABG (n = 610) or medical management (n = 602) in the STICH (Surgical Treatment for Ischemic Heart Failure) trial. Mortality (n = 462) was compared by treatment allocation during 56 months (interquartile range: 48 to 68 months) of follow-up for subjects able (n = 682) and unable (n = 530) to walk 300 m in 6 min and with less (Physical Ability Score [PAS] >55, n = 749) and more (PAS ≤55, n = 433) limitation by dyspnea or fatigue. RESULTS: Compared with medical therapy, mortality was lower for patients randomized to CABG who walked ≥300 m (hazard ratio [HR]: 0.77; 95% confidence interval [CI]: 0.59 to 0.99; p = 0.038) and those with a PAS >55 (HR: 0.79; 95% CI: 0.62 to 1.01; p = 0.061). Patients unable to walk 300 m or with a PAS ≤55 had higher mortality during the first 60 days with CABG (HR: 3.24; 95% CI: 1.64 to 6.83; p = 0.002) and no significant benefit from CABG during total follow-up (HR: 0.95; 95% CI: 0.75 to 1.19; p = 0.626; interaction p = 0.167). CONCLUSIONS: These observations suggest that patients with ischemic left ventricular dysfunction and poor exercise capacity have increased early risk and similar 5-year mortality with CABG compared with medical therapy, whereas those with better exercise capacity have improved survival with CABG. (Comparison of Surgical and Medical Treatment for Congestive Heart Failure and Coronary Artery Disease [STICH]; NCT00023595).