A comparison of the short and long term outcome in two groups of patients admitted to hospital during the acute phase of their first myocardial infarction, an anterior group (123 cases) and a posterior group (147 cases) has produced the following results:--an immediate mortality which was significantly higher (identical cause of death) in the anterior infarct group (22.8%) than in the posterior infarct group (11.6%): p less than 0.02;--a very similar long term mortality (5 to 6% per year) in the two groups (the main causes for which cannot be equated) despite the fact that the initial destruction of muscle was usually greater when the infarct had been anterior. These results seem to lead to the following conclusion: a better overall prognosis seems to be related to efforts to limit the extent of an infarct, especially when it is anteriorly situated; sometime after the infarct, it is also linked to the improvement in vascularity of the regions which are not involved, especially in cases of posterior necrosis.