Background: The delay in O2 uptake kinetics during and after submaximal physical activity (O2 onset and recovery kinetics, respectively) correlates well with the functional capacity of patients with chronic heart failure (CHF). This study examined the physiological background of this delay in moderately impaired CHF patients by comparing kinetics of cardiac output (Q?) and O2 uptake (V?O2 ). Methods: Fourteen stable CHF patients (New York Heart Association class II-III) and 8 healthy subjects, matched for age and body mass index, were included. All subjects performed a submaximal constant-load exercise test to assess O2 uptake kinetics. Furthermore, in 10 CHF patients Q? was measured by a radial artery pulse contour analysis method, which e...