Comparison of the short term clinical course of 2 groups of patients who had suffered a first posterior myocardial infarction complicated during the acute phase (group A) by 2nd or 3rd degree atrioventricular block, or free of such a complication (group B), confirmed two classical concepts: the onset of this complication in one case out of five and a two-fold increase in mortality when it occurs. In the mid- and long term, however, the course is relatively similar in both groups, which do not differ initially in terms of average age, sex distribution nor the usual risk factors of coronary artery disease. In addition, the absence of sudden deaths in group A would suggest that AV block is a definitively regressive complication.