Although many different drugs and interventions have been studied in cardiac arrest to improve survival rates and neurological outcome, the results are still very poor. Magnesium (Mg) has important electrophysiological effects and normal concentrations are required to maintain regular cardiac conduction, rhythm and vascular tone, but its role in improving survival rates and neurological outcome in victims of cardiac arrest is not completely understood. We conducted a systematic review to identify evidence regarding the role of Mg in cardiac arrest. Specifically, we looked for data to answer if survival rates and neurological outcome are related to the administration of Mg either during CPR or following return of spontaneous circulation. We found that there are very few data available about the role of Mg in the treatment of cardiac arrest. Although two non-randomised and one animal study reported promising results, the lack of high quality studies makes it impossible to recommend for or against the administration of Mg during or early after resuscitation to improve outcome.