Until recently, randomized studies of implantable cardioverter defibrillator (ICD) have only included patients with a remote history of myocardial infarction (MI). Two studies evaluated the use of ICDs early following MI, the DINAMIT and BEST+ICD studies, but failed to demonstrate significant reduction in mortality. Current guidelines therefore recommend deferring ICD implantation for at least 40 days following MI. This article highlights the limitations of these two studies and reviews the application of the '40-day' rule to patients with acute MI.