Designed to give healthcare professionals an introduction to potassium and the heart. It reviews the role of this important electrolyte in health and disease. Disturbances in potassium are common and, while patients may be asymptomatic, it can be life threatening. Patients with chronic kidney disease or heart failure patients receiving renin-angiotensin-aldosterone system inhibitors are particularly vulnerable. This module highlights aspects of the identification of potassium abnormalities, and how these may be treated acutely and in the chronic setting.