The current study aimed to test sensation seeking as a mediator in the relationship between arousal and aggression. In addition, an experimental design was used to test whether arousal can be manipulated to alter levels of sensation seeking and aggression, both measured behaviorally. A sample of 128 undergraduate students completed state and trait measures of sensation seeking and aggression, and baseline measures of physiology. It was hypothesized that trait sensation seeking would mediate the relationship between baseline physiology and trait aggression. Also, state sensation seeking would mediate the relationship between an arousal manipulation and state aggression. The results failed to support the proposed mediation models. Furthermore, the arousal manipulation was insufficient to result in sustained heart rate differences, and therefore the malleability of state sensation seeking and aggression could not truly be tested. Exploratory analyses supported an interaction between arousal and sensation seeking, such that in individuals low on experience seeking, disinhibition and boredom susceptibility, low heart rate was associated with greater aggression. These findings suggest that arousal and sensation seeking may conjointly predict aggression through moderation rather than mediation, though future studies with improved experimental designs are needed.