Two experiments with N = 221 university students investigated the impact of primed cognitive conflict on effort assessed as cardiac response in tasks that were not conflict-­ related themselves. Manifest cognitive conflict in cognitive control tasks is confounded with objective response difficulty (e.g., in incongruent Stroop task trials). This makes conclusions about the effortfulness of cognitive conflict itself difficult. We bypassed this problem by administrating pictures of congruent versus incongruent Stroop task stimuli as conflict primes. As predicted, primed

cognitive conflict increased cardiac pre-­ ejection period (PEP) responses in an easy attention task in Experiment 1. Accordingly, cognitive conflict itself is indeed effortful. This effect was replicated in an easy short-­ term memory task in Experiment 2. Moreover, as further predicted, the primed cognitive conflict effect on PEP reactivity disappeared when participants could personally choose task characteristics. This latter effect corresponds to other recent evidence showing that personal action choice shields against incidental affective influences on action execution and especially on effort-­ related cardiovascular response.