The purpose of the present investigation was to examine the association between cardiovascular reactivity to provocation and physically and relationally aggressive conduct. Blood pressure and heart rate were assessed among seventy-seven 5th-grade participants during a period of rest and while discussing a relational provocation. In addition, teachers reported on participants' physically and relationally aggressive behavior. Results provided support for the hypothesis that heightened cardiac reactivity to provocation would be associated with relational forms of aggression among girls. In contrast, for boys, lower cardiac reactivity was associated with physical aggression. These results suggest that the association between cardiovascular reactivity and aggression differs for males and females and that reactivity following relational provocation may be an especially important predictor of relational aggression among girls. Implications for interventions among aggressive children are discussed.