Multilevel inhibition of neurohormonal activation using angiotensin-converting enzyme inhibitors, beta-blockers, angiotensin receptor blockers, and aldosterone antagonists is the cornerstone of modern heart failure treatment. Use of these agents in optimal doses is associated with significant improvements in heart failure-associated morbidity and mortality but also may increase serum potassium. Because potassium excretion already is impaired in many heart failure patients because of advanced age, diabetes, or chronic kidney disease, the risk of life-threatening hyperkalemia during treatment is significant. This review discusses the mechanisms, incidence, predictors, and management of hyperkalemia in heart failure, emphasizing the importance of careful patient selection for medical treatment and regular surveillance of potassium and creatinine.