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A total of 266 patients entered into a study comparing the effect of intravenous magnesium and propranolol following acute myocardial infarction. Of these, 97 were able to receive either drug and were therefore randomized into the magnesium (n = 51) or propranolol group (n = 46). 88 patients were unable to receive propranolol and formed a third group (NR) while a further 81 patients could not receive either drug and formed a fourth group (N). The study showed that intravenous magnesium was as effective in preventing potentially lethal arrhythmias as propranolol and could be given to some 70 per cent of such patients whereas propranolol could only be given to 36 per cent.

Ninety-five patients with acute myocardial infarction were followed up for 6 months to 3 years (mean 25.4 months) in a preliminary study to compare the effects of intravenous magnesium (49 patients) with that of intravenous propranolol (44 patients) given immediately after admission to the intensive care unit. There were four cardiac deaths in the propranolol group and no deaths in the magnesium group (P0.046) and 27 per cent of patients who received propranolol subsequently developed cardiac failure as opposed to 12 per cent of those who had received magnesium (P0.04). Intravenous magnesium given in the early stages of myocardial infarction reduces the subsequent cardiac death rate possibly by reducing infarct size.