We extend the logic of Haselton and Buss's (2000) error management theory to the domain of social exchange and propose that a psychological mechanism, referred to as the social exchange heuristic (SEH), produces certain cognitive biases that affect how individuals manage these errors. We predicted that the SEH would remain dormant in individuals who failed to realize that they were in a situation that involved social exchange. In the first experiment (n = 78), PD players who had a chance, before they played the game, to think both about the nature of the game they were playing and about their partner's choice were less cooperative compared to players of the standard one-shot PDG. In the second experiment (n = 105), PD players were again less cooperative when they made their decision before they were matched with a particular partner than after they had been matched with a partner. Results strongly suggest the operation of a SEH.