Potassium is the main intracellular ion and its homeostasis is finely regulated by the renal and gastrointestinal tract. Renal failure and hyperkalemia are conditions commonly found in patients with heart failure, the result of a complex interaction between heart and kidney (e.g. cardio-renal syndrome) and the side effects of drugs commonly used for treating heart disease (e.g. renin-angiotensin-aldosterone system inhibitors). Although hyperkalemia increases the risk of heart conduction disorders and life-threatening arrhythmias, its prognostic significance in heart failure is uncertain. Hyperkalemia and progression of renal damage are the main limitations to the introduction and titration of heart failure therapies. New drugs for the prevention and chronic treatment of hyperkalemia allow the introduction and modulation of anti-neurohormonal therapies in patients with heart failure otherwise excluded from these treatments due to excessively high serum potassium levels.This review illustrates the pathophysiological, epidemiological and prognostic aspects of hyperkalemia and analyses the possible treatments for this condition in heart failure patients.