Many years ago, experimental medicine accumulated substantial evidence that magnesium (Mg) balance was important for a stable cardiovascular system. Recent clinical interest was aroused by evidence of decreased mortality in patients with acute myocardial infarction (AMI), treated with Mg infusions. Pharmacologic actions of Mg include its antiarrhythmic, antivasospastic and other important cardiovascular effects, substantiating the rationale for its use in AMI. Direct pharmacologic effect of this ion, rather than compensation of hypomagnesemia frequently encountered during acute ischemic injury, has been suggested to account for the above benefits. Several trials studied the efficacy of early Mg therapy in decreasing mortality from AMI while most of the data point to improved survival, a few trials could not demonstrate any benefit of Mg. The reported rate of complications with this therapy is low though the potential for serious side effects exists. Larger studies of Mg in AMI are expected to resolve the existing controversy.