The present study tested the hypothesis that internal as compared with external locus of control Ss would show reliably greater self-control of heart rate (HR) slowing, as well as speeding, when given a longer period of training than was used in previous studies. Thirty-eight male volunteer Ss (19 internals and 19 externals) were instructed to control HR and received continuous visual feedback of cardiac rate during three series of trials, followed by a no-feedback transfer series. During each series Ss attempted to raise HR on five trials and to lower it on five trials. Directional control of HR was demonstrated, and the changes were sustained with feedback removed. Internals were superior at raising HR during the first series and improved consistently across subsequent series including no-feedback, whereas externals showed small increases of comparable magnitude across each series. No significant differences between the internal and external groups were noted for slowing, although internals showed a trend toward improved control across series. Changes in respiration rate, eye blinking, and self-reported tension-relaxation, as well as control strategies, were described. Group differences in cardiac self-control were discussed in relation to the motivational and cognitive processes that differentiate an internal from an external, and to possible differences in reactivity of the cardiovascular system. It was concluded that externals are not better able to decrease HR as previous studies suggested, but that extended training will be required to demonstrate internal superiority at slowing HR.