Hyperkalemia is a life-threatening electrolyte derangement that can lead to fatal ventricular dysrhythmias and subsequent sudden cardiac death. There are many underlying causes that can cause hyperkalemia, but they can be simplified into three overarching etiologies: excess potassium intake [e.g., potassium-containing intravenous fluids, total parenteral nutrition (TPN)], disruptions in balance between intracellular and extracellular potassium balance (e.g., rhabdomyolysis, tumor lysis syndrome, succinylcholine), and derangements in potassium excretion (e.g., renal dysfunction, hypoaldosteronism, mineralocorticoid deficiency). In practice, hyperkalemia often manifests in critically ill patients as a multifactorial consequence of underlying acute pathology and chronic comorbidities. Prompt recognition and treatment are essential in the emergency department setting to initiate temporizing measures while appropriately dispositioning the patient to a level of care that will allow for cardiac monitoring and, if necessary, hemodialysis to definitively lower serum potassium levels.