Kir2.1 is a member of the family of inward rectifying K+ channels. The family includes 15 members that are structurally and functionally different from the voltage-dependent K+ channels.Kir2.1 is a member of the Kir2.x subfamily that includes four members (Kir2.1- Kir2.4) that are characterized by strong inward rectification and high constitutive activity.nKir2.1 is expressed in a variety of tissues including heart, brain, vascular smooth muscle cells and skeletal muscles.nIn heart, Kir2.1 is a molecular component of the IK1 current that is responsible for setting the resting membrane potential, preventing membrane hyperpolarization due to Na+ pump activity, influencing propagation velocity, altering the electrical space constant, and promoting late phase repolarization.2 In fact, mutations in Kir2.1 channels have been linked to a form of long QT syndrome (LQT7) known as Andersen's syndrome that is characterized by cardiac arrhythmias, periodic paralysis, and dysmorphic features.