The aim of this review is to present the properties of the slow component of the delayed rectifier potassium current (IKs) in the human ventricle. The review gives a detailed description of the physiology, molecular biology and pharmacology of the IKs current, including kinetic properties, genetic structures, agonists and antagonists. The authors also present the role of the IKs current in the human cardiac repolarization focusing on several pathophysiological situations, such as the LQT syndrome and the Torsade de Pointes arrhythmia.