Several studies in multimedia learning have examined the effect of emotional design. Recent findings from cognitive psychology provide opportunities for educators to use more direct ways of manipulating emotion to enhance learning. These studies have shown that emotionally arousing words and pictures are remembered better than neutral ones. Building upon these findings, this experimental study investigates the effect of arousal of instructional materials on learning. A total of 154 participants were randomly divided into a "high-emotional arousal" and a "low-emotional arousal" group in a between-subjects design. These results suggest that emotional arousal enhanced learning. Mediation analyses show that the effect of arousal on learning was partially mediated by interest. Accordingly, emotional arousal increased interest, which in turn improved transfer scores. The findings imply that motivational factors such as situational interest encouraged elaborative processing and deeper levels of learning. The direct effect of emotional arousal on learning was also significant.