Identity fusion is a feeling of oneness with the group that induces people to tether their feelings of personal agency to the group. We accordingly proposed that increasing the agency of fused persons by elevating autonomic arousal would amplify their tendency to endorse and actually enact pro-ingroup behavior. In 4 experiments, increasing autonomic arousal through physical exercise elevated heart rates and fusion-unrelated activity among all participants. Fused participants, however, uniquely responded to arousal by translating elevated agency into endorsement of pro-group activity. These effects emerged both for endorsement of extreme behaviors for the group and for overt behaviors, specifically helping behavior (donating money to needy in-group members), and the speed with which participants raced a fusion-related avatar. The effects also generalized across 3 different arousal inductions (dodgeball, wind sprints, and Exercycle). Finally, fusion-related agency partially mediated the interactive effects of fusion and arousal on pro-group behavior. Apparently, autonomic arousal increases agency and identity fusion channels increased agency into pro-group behavior.