The present study explores emotional, relational, and communicative responses to different-sex and same-sex infidelity in heterosexual romantic relationships. Two-hundred and eighty-five men and women completed an online survey. Individuals were asked to read a scenario in which an imagined heterosexual partner engages in infidelity with a different-sex or same-sex person. Individuals were randomly assigned to one of these two conditions and then asked to complete several measures assessing their imagined emotions, communicative responses, and relational outcomes. Results revealed that both men and women experienced more negative emotional responses to different-sex infidelity versus same-sex infidelity. Additionally, men reported more sexual arousal in response to a woman's same-sex infidelity versus different-sex infidelity, while women's sexual arousal did not vary across conditions. Lastly, men's communicative responses to jealousy (CRJs) for same-sex and different-sex infidelity did not vary, though women reported that they were more likely to respond to same-sex infidelity than different-sex infidelity with denial, and more likely to respond to different-sex than same-sex infidelity with signs of possession. Several emotional responses to same-sex infidelity were also found to predict various CRJs. These findings and the implications of the study are discussed.