A strong body of existing research highlights the importance of considering heterogeneity in entrepreneurial team composition. Adding to this stream of research, we focus on the effects of heterogeneity in team members’ individual entrepreneurial orientation (iEO). Drawing on theories of social psychology and organizational behavior, we argue that iEO heterogeneity negatively affects team performance. Additionally, we propose a moderated mediation approach to shed light on the black box of the heterogeneity-performance relationship. We argue that relationship conflict is a partial mediator of this pivotal relationship. Furthermore, we argue that emotional intelligence bears the potential to reduce negative effects of heterogeneity.