Investigated the effects of locus of control on voluntary control of heart-rate change. The 32 subjects were randomly assigned to one of two heart-rate change groups: Increase or decrease. The groups were counterbalanced for locus of control and sex. No heart-rate feedback was provided to subjects, and all subjects performed the appropriate task for two sessions. Results indicated that during the initial session, internals were better able to increase their heart-rates than externals; the externals were better able to decrease their heart-rates than internals. This association, however, diminished to nonsignificance in the second session.