['Rate adaptive pacing (RAP) during cardiac resynchronisation therapy (CRT) in patients with chronic heart failure (CHF) might improve exercise capacity through enhanced cardiac output (CO). Conversely, higher heart rates (HR) might set off a blunted force-frequency response (FFR).', 'Fourteen CRT-treated patients (62+/-3 years, left ventricular ejection fraction 30.8+/-2.7%) underwent two cardiopulmonary exercise tests (CPET). CPET1: rate response off; CPET2: rate response on. Conventional and tissue doppler echocardiography were obtained at rest and at peak exercise.', 'Peak values for HR (106+/-5 vs. 127+/-3 bpm; P=0.001) and CO (6.4+/-0.4 vs. 7.4+/-0.4 l/min/m; P=0.001) increased significantly comparing CPET1 and CPET2. Stroke volume index (28.8+/-1.4 vs. 27.9+/-1.2 ml/m, P=0.2) and peak oxygen consumption (17.8+/-0.9 vs. 17.4+/-0.7 ml/kg/min, P=0.6), however, did not differ. Longitudinal systolic velocities of the basal septum (SSm: 6.9+/-0.9 vs. 6.1+/-0.8 cm/s, P=0.07), basal left lateral (LSm: 6.1+/-1.3 vs. 5.9+/-0.8 cm/s, P=0.3) and basal right ventricular free wall (RVSm: 11.7+/-0.9 vs. 10.1+/-0.7 cm/s, P<0.01) remained unchanged or decreased. Inter-ventricular (Deltat LSm-RVSm) (10+/-18 vs. 15+/-9 ms) and intra-ventricular mechanical delay (Deltat SSm-LSm) (10+/-15 vs. 9+/-6 ms) did not change.'] Does rate response and cardiac resynchronisation therapy in chronic heart failure : higher cardiac output acutely improve exercise performance : a pilot trial?