The majority of studies investigating the relationships between psychological characteristics and cardiovascular reactivity to stress use a research strategy in which discrete traits are evaluated in isolation. The present study examined the effects of additive and/or interactive relationships among traits on cardiac reactivity to a mental arithmetic task. In addition, impedance cardiographic techniques were employed to examine potential relationships between such psychological traits and a specific measure—pre-ejection period (PEP)—of sympathic influence on the heart. Forty-nine undergraduate men performed a mental arithmetic task while continuous measures of PEP and interbeat interval (IBI) were collected. The subjects then completed questionnaires measuring anger expression, hostility, and trait anxiety. Analyses of variance (ANOVAs) showed a significant main effect for anger-out on PEP change from baseline, but not for IBI. Results also showed that anger-in interacted with anger-out and hostility to affect both PEP and IBI changes significantly. Other results indicated that subjects in the high anger-in/low anger-out and high anger-in/low hostility groups did not show significant PEP change, although they nevertheless showed significant IBI change. These results highlight the importance of the consideration of interactions among traits in predicting cardiac reactivity and of the importance of measuring specific indexes of sympathetic arousal.