It has been suggested that internists and family practitioners have somewhat different "disease" perspectives, which may be generated by use of different explanatory models during medical training (pathophysiological vs. biopsychosocial, respectively). This article explores differences between internists and family practitioners in their suggested diagnoses, level of diagnostic certainty, test and prescription ordering, when encountering exactly the same "patient" with coronary heart disease (CHD). Internists were more certain of a CHD diagnosis than family practitioners and were more likely to act on this diagnosis. Family practitioners were more likely to diagnose (and were more certain of) a mental health condition. While many physicians simultaneously entertain several alternate diagnoses, diagnostic certainty has shown to have an important influence on subsequent clinical actions, such as stress testing and prescription of beta blockers. These results may inform future educational strategies designed to reduce diagnostic uncertainty in the face of life-threatening conditions, such as CHD.