16 male and 16 female undergraduates played a mixed-motive game against a male confederate under either a 20 or an 80% cooperative strategy while cardiovascular responses were computer monitored. Females had larger heart rate responses than males during play under the competitive strategy, and the opposite was true during play under the cooperative strategy. Ss who were more competitive during the game, who scored higher on a coronary-prone (Type A) behavior scale, or who reported having an action orientation toward life stress tended to have larger heart rate responses during the game than did the remaining Ss. Results draw attention to the importance of covert autonomic responses for understanding overt behavioral choices in mixed-motive games and to the potential utility of this behavioral model for studying the role of psychosocial factors in psychosomatic illnesses. (21 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1979 American Psychological Association.