Severe hyperkalemia is a life-threatening electrolyte disorder that causes an increase of all-cause mortality and increases the risk of arrhytmias. Hyperkalemia is common in the case of certain predisposing conditions such as chronic kidney disease, type II diabetes and RAASi treatment. ECG is insensitive in assessing severity of hyperkalemia. New oral unabsorbable potassium binding agents (ZS-9, patiromer) bind potassium in the gastrointestinal tract to facilitate fecal excretion. This might increase effectiveness and safety in treating acute and long-term hyperkalemia, also in patients with chronic kidney disease and heart failure, who are undergoing RAASi treatment. The purpose of this review was to give an overview of the incidence, etiopathogenesis, diagnostics and treatment of hyperkalemia.