Broaden and build theory (BBT; Fredrickson, 1998; 2001) postulates that positive emotions expand the scope of one's attention and thought-action repertoires (Fredrickson & Branigan, 2005). Within the boundaries of BBT, the undoing hypothesis (Fredrickson, 1998, Fredrickson & Levenson, 1998) argues that positive emotions themselves do not bring forth specific action tendencies or urges; therefore, they do not consequently require an increase in cardiovascular activity to carry out the urge. On the other hand, positive emotions have evolved to subdue the cardiovascular response previously initiated by negative emotions. This dissertation proposes that the real power of positive emotions might be to undo not the effects of negative emotions themselves, however, but simply reduce the arousal itself. This dissertation used minor physiological arousal (e.g., a step-stool task) to simulate the cardiovascular effects of the stress manipulations used in previous tests of the undoing hypothesis by Fredrickson and colleagues. This dissertation asks if positive emotions undo the cardiovascular reactivity of an emotionally neutral stimulus. Positive emotions were induced through one film clip (i.e., a happy film clip) and was compared to a neutral film clip (no emotion elicited). An experimental design measured the effects of arousal induction and film clip on participants' cardiovascular activity. Results indicated that positive emotions had the same effect as no emotions on participants' cardiovascular activity. Implications for theory and research are provided, as well as an assessment of the study's strengths and limitations. Finally, several directions for future research are offered.