Patients with heart failure (HF) frequently have an impaired heart rate response to exercise and reduced oxygen consumption (VO(2)). Cardiac resynchronization therapy (CRT) has been shown to increase functional capacity in patients with HF and conduction delay. However, detailed analysis of improvement in functional capacity after CRT is still lacking. This study aimed to provide a detailed analysis of the changes in metabolic, ventilation parameters, and heart rate profiles in patients with HF and ventricular conduction delay following implantation with resynchronization devices. We provided a retrospective review on 50 patients in New York Heart Association functional class >II, with left ventricular ejection fraction <35%, on optimal medical therapy, and whose functional capacity was evaluated by cardiopulmonary exercise testing before and after CRT. Detailed analysis of VO(2), carbon dioxide production (VCO(2)), heart rate, minute ventilation (V(E) [liters per minute]), tidal volume (V(T)), respiratory rate, and heart rate profile during exercise were performed. Following CRT, peak VO(2) increased significantly from 14 +/- 4 to 17 +/- 4 (p <0.0001), and VO(2) at anaerobic threshold increased from 9 +/- 2 to 12 +/- 3 (p <0.001). All ventilation and metabolic parameters significantly increased following CRT. Similarly, heart rate at rest significantly decreased after CRT (76 +/- 12 vs 72 +/- 12 beats/min, p <0.05), whereas the maximum achieved heart rate increased significantly from 119 +/- 20 to 125 +/- 24 beats/min (p <0.05). The proportion of patients with chronotropic incompetence was significantly reduced after CRT (50% before CRT vs 34.7 after CRT; p <0.05). Patients with the baseline peak VO(2) <14 ml/kg/min benefited most from the implantation of a CRT device. In conclusion, CRT significantly improves all ventilation and metabolic parameters of patients with HF and conduction delay. Patients with more depressed metabolic and ventilation parameters and higher heart rate at baseline seem to benefit most from this therapeutic approach.