Hyperkalemia is mainly caused by decreased renal potassium excretion but can also result from increased intake or cellular translocation. It affects water and electrolyte balance, with serum levels serving as a key diagnostic indicator. Elevated potassium levels (>6.5 mEq/L) can lead to serious cardiac disturbances such as bradycardia, necessitating urgent treatment when levels exceed 7.5 mEq/L. Management includes identifying and treating the underlying cause, with therapies such as insulin, bicarbonate, and terbutaline. Careful monitoring of potassium, especially in patients on certain medications or with renal impairment, is essential to prevent life-threatening complications.