The purpose of this pilot interventional study is to collect preliminary data on administering magnesium sulfate as a neuroprotective medication in patients who achieved Return of Spontaneous Circulation (ROSC) following Cardiac Arrest (CA). The primary aims are to assess the feasibility and safety of administering magnesium and measure serum markers of neuronal injury at prespecified time points in the post-cardiac arrest period. Because this is a pilot study with a limited sample size, the primary objective is to evaluate the precision and stability of the collected measures to inform the design and formal analysis in a larger trial.