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STUDY OBJECTIVE: To investigate the prognostic value of oxygen uptake (O(2)) kinetics during low-intensity exercise in patients with congestive heart failure. DESIGN: Prospective cohort study. SETTING: Tertiary care center. PATIENTS: One hundred forty-six consecutive patients (128 men) with chronic heart failure, followed up for a mean (+/- SD) duration of 25 +/- 15 months. MEASUREMENTS: A treadmill exercise test was performed with "breath by breath" gas-exchange monitoring. VO(2) kinetics were defined as the VO(2) deficit (ie, Delta VO(2) x time[rest to steady state] - Sigma VO(2)[rest to steady state]) and mean response time (MRT) [ie, VO(2) deficit/Delta VO(2)]. Cardiac death, urgent cardiac transplantation, and hospitalization due to worsening heart failure were considered as the end points. RESULTS: Thirty patients (21%) died, 11 patients (8%) underwent urgent transplantation, and 32 patients (22%) were hospitalized. In univariate analysis, MRT was the most powerful predictor of survival, survival free of urgent transplantation, and survival free of hospitalization (hazard ratios [HRs] per 10 s, 1.65, 1.72, and 1.61, respectively; all p < 0.0001). The predictive value of MRT exceeded that of peak VO(2) (HR per mL/kg/min, 0.90; p = 0.02, 0.91; p = 0.007, and 0.95; p = 0.08, respectively). In multivariate analysis, MRT (HR per 10 s, 1.73; p = 0.0002), resting systolic BP (HR per 10 mm Hg, 0.65; p = 0.003), and the slope of the ventilatory response to exercise (HR per 10 U, 1.68; p = 0.02) were independent predictors of survival. CONCLUSIONS: Our results suggest that VO(2) kinetics are strongly related to outcome in heart failure patients. Since it has several additional advantages over peak exercise testing (eg, less time-consuming, less demanding for the patients, less dependent on motivation, and applicable in patients with limitations other than cardiopulmonary disease), it has the potential to become a prognostic test for the assessment of heart failure patients.