This article reviews the effects of changes of heart rate on the ventricular action potential duration. These can be divided into short term (fractions of a second), resulting from the kinetics of recovery of membrane currents, through to long term (up to days), resulting from changes of protein expression. We concentrate on the medium‐term changes (time course of the order of 100 s). These medium‐term changes occur in isolated tissues and in the intact human heart. They may protect against cardiac arrhythmias. Finally, we discuss the cellular mechanisms responsible for these changes.