This investigation compares the cardiovascular responses of normal (n = 10) and cardiac transplant (n = 14) subjects to peak arm and leg exercise. It also tests the hypothesis that the higher heart rate (fc) in normal subjects during light (30 W) submaximal arm versus leg exercise is due to cardiac innervation. In cardiac transplant patients, power output, oxygen consumption (VO2), fc and rate pressure product were 54%, 28%, 7%, and 8% lower during peak arm than leg exercise, respectively. In normal subjects, power output, VO2, fc and rate pressure product were 61%, 33%, 8%, and 11% lower during peak arm than leg exercise, respectively. In cardiac transplant patients there was no significant difference in absolute fc during submaximal arm and leg exercise. In normal subjects, absolute fc during arm and leg exercise was [mean (SD)] 97 (4) beats.min-1 and 92 (4) beats.min-1, respectively (P = 0.07). Plasma noradrenaline was increased more during arm than leg exercise in both cardiac transplant and normal subjects. Maximal leg testing is useful when determining the capacity of cardiac transplant patients to perform arm work. The higher absolute fc reported by other investigators for normal subjects during submaximal arm versus leg exercise may be mediated by cardiac innervation.