The risk of hyperkalaemia in patients with heart failure has increased in the past few years together with the evolution of pharmacological treatment for these patients. This significant change has been associated with the introduction of angiotensin converting enzyme (ACE) inhibitors, angiotensin II receptor blockers (ARBs), and aldosterone antagonists. High potassium concentrations in heart failure could lead to life threatening events, and therefore should be taken seriously. In this review we summarise the information about potassium homeostasis in heart failure and the current risk of developing potentially serious hyperkalaemia, particularly in association with the use of aldosterone antagonists.