BACKGROUND Left ventricular assist devices (LVADs) are frequently used as a bridge to cardiac transplantation and may be useful as long-term therapy. The purpose of this study was to compare the exercise performance of LVAD patients with that of ambulatory heart failure patients. RESULTS Exercise testing with hemodynamic and respiratory gas measurements was performed in 65 congestive heart failure (CHF) patients (age 53+/-10 years) and 20 LVAD patients (age 49+/-8 years). Peak Vo2 was significantly higher in the LVAD than the CHF patients (CHF, 12+/-3; LVAD, 15. 9+/-3.8 mL . kg-1 . min-1; P<0.001), as was the Vo2 at the anaerobic threshold (CHF, 8.1+/-2.1; LVAD, 12.2+/-2.9 mL . kg-1 . min-1; P<0.001). At rest, mean arterial blood pressure (CHF, 87+/-11; LVAD, 94+/-9 mm Hg) and cardiac output (CHF, 4+/-1; LVAD, 4. 9+/-0.9 L/min) were increased, whereas mean pulmonary artery pressure (CHF, 28+/-11; LVAD, 18+/-4 mm Hg) and pulmonary artery wedge pressure (CHF, 16+/-10; LVAD 5+/-3 mm Hg) were reduced (all P<0.01). At peak exercise, heart rate (CHF,125+/-24; LVAD, 148+/-24 bpm), blood pressure (CHF, 87+/-14; LVAD,96+/-12 mm Hg), and cardiac output (CHF, 7.6+/-2.2; LVAD, 11.2+/-2.6 L/min) were higher (all P<0. 01), whereas mean pulmonary artery pressure (CHF, 48+/-12; LVAD, 30+/-5 mm Hg) and mean pulmonary capillary wedge pressure (CHF, 31+/-11; LVAD, 14+/-6 mm Hg) were lower in the LVAD group (both P<0. 001). In the LVAD patients, Fick cardiac output was higher than LVAD flow sensor value measurements (Fick, 11.6+/-2.5; LVAD, 8.1+/-1.2 L/min; P<0.001). CONCLUSIONS Hemodynamic measurements at rest and during exercise are significantly improved in patients with devices compared with those in ambulatory heart failure patients awaiting cardiac transplantation. Similarly, the exercise capacity of device patients is better than that of transplant candidates and in the majority of patients is similar to that of patients with mild CHF.