Purpose: Incidentally-detected, growing, asymptomatic abdominal aortic aneurysms (AAA) present a challenging treatment decision, but not one without statistical guidelines. Elective surgery for AAA comes with a mortality risk of approximately 5%. Untreated AAA have an annual expansion range 0.2 - 0.4 cm and growing risk of a fatal rupture. Our work with surgeons shows that, even when equipped with statistical guidelines, presenting a simulation of an early AAA rupture during watchful waiting (WW) leads them to send a subsequent simulated AAA patient to surgery earlier. We hypothesize that a major causal mechanism behind this effect is the surgeon's anxiety caused by this negative outcome in a previous patient. Methods: This experiment utilized participants, in the role of surgeon, performing the same computer-based AAA simulation performed by surgeons, in which an AAA rupture, surgical mortality, or no bad outcome are demonstrated before the simulation. To test the nature of this decision effect, emotions were measured at different time points during the experiment. Participants answered the State-Trait Anxiety Inventory State 6-Item Short Form (STAI-6) at the beginning of the experiment and again immediately following the experimental manipulation. Additionally, the participants' assessments of emotional valence, arousal, and dominance in response to the AAA watchful waiting rupture simulation were evaluated using the methods of the International Affective Picture System (IAPS) along with a number of IAPS images. Results: Results (N=77) of the STAI-6 indicate that the watchful waiting rupture condition elicited a significantly larger mean increase (2.86) in anxiety from pre to post manipulation than did the control group (0.50) that observed no bad outcome (F = 3.45, p<.04, partial ç2 = .10). Additionally, participants rated the AAA simulation as highly negative, moderately arousing, and dominating on IAPS ratings, similar to ratings of an image of an child with an eye tumor. Participants did not exhibit good memory for the details of the demonstration AAA, with only 44% recalling their number WW decisions and 26% recalling the final AAA size. Conclusions: The presentation of an unexpected WW AAA rupture causes elevated anxiety, and this is likely the cause of the previously demonstrated effect of surgeons' hastened decision to go to surgery. This effect is not largely cognitive, as participants did not exhibit accurate memory of details of the demonstration AAA.