There has been some debate regarding the benefit of parenteral magnesium (Mg) in the treatment of acute myocardial infarction (AMI), due to conflicting results from animal studies and recent clinical trials. Several different hypotheses, proposing antiplatelet, and antithrombotic properties have been advanced to explain the cardioprotective properties of Mg during AMI. Although early clinical results were promising, there were serious flaws in the design and the logistics of small trials including out of date methodology, absence of control groups, and possible observer bias due to unblinded data collection. Moreover, the latest large-scale megatrial Fourth International Study of Infarct Survival (ISIS-4) provided conflicting data and caused major controversy, which will be difficult to resolve. Proponents of Mg therapy have suggested that the potential benefit was not seen in ISIS-4 because Mg was administered too late. Further clinical trials, well-designed, and carefully conducted, should elucidate possible benefits of parenteral Mg during myocardial injury, especially in conjunction with new and aggressive reperfusion techniques. The benefits of parenteral Mg in an expanding array of clinical conditions, including AMI, may be directly related to an improved hemostatic profile. This review summarizes the latest, and often confusing data on the effects of Mg on certain hemostatic characteristics which may be directly relevant to the existing controversy.