The trials reviewed in this study investigated the effect of intravenous magnesium on arrhythmias and mortality in acute myocardial infarction. Nine trials were carried out in the pre-thrombolytic era. They varied in set-up, number of patients, dose of magnesium, follow-up and the type of arrhythmias analyzed. Magnesium reduced mortality in most studies, but the reduction was significant in only three of them. Two meta-analyses of the smaller studies revealed a 55% reduction in mortality. In the LIMIT-2, in which 2300 patients were enrolled, magnesium reduced mortality significantly by 24%. The effect of magnesium on arrhythmias was less clear. Preliminary results of ISIS-4, in which magnesium among others was administered together with thrombolytic agents, did not provide evidence of benefit in patients with suspected myocardial infarction. At present there are no arguments for the use of magnesium in acute myocardial infarction.