In today's socially connected world marketers are turning to social video as a way of extending campaign reach and gaining cut-through. However knowledge on which creative characteristics are related to successful diffusion, is limited. In this research we consider how two constructs of emotional response (arousal and valence), both separately and collectively are related to how videos are shared. Two large data sets are considered, one commercial and one non-commercial ( n800), with levels of actual daily sharing recorded for all videos examined. We find that high arousal emotions are the primary driver of video sharing and while valance plays a role, it does so to a lesser extent. This study is the largest of its kind and makes a significant contribution to our understanding of what makes a successful viral video.