In a previously reported canine model of sudden cardiac death, its authors heavily weighted the role of the autonomic nervous system in determining whether or not a combined stress of submaximal exercise and ischemia would produce a fatal arrhythmia the setting of a healed anterior wall myocardial infarction. This morphologic study of that model reveals that anatomic factors are also relevant to vulnerability to sudden death: dogs who developed ventricular fibrillation in response to such a stress (susceptible) had significantly more of the left ventricle (LV) infarcted than dogs who survived the stress (resistant): 13.14% (+/- 2.67 S.E.M.) as compared with 4.01% (+/- 2.11 S.E.M.). Moreover, areas of fibrosis were spread more widely throughout the ventricle and septum in susceptible as compared with resistant animals, which consistently showed more homogeneous areas of infarct largely confined to the apical portion of the LV. While the autonomic nervous system may well be relevant to survival to stress in an animal which has survived a myocardial infarction, we conclude that there are important anatomic factors which determine vulnerability.