Esmolol is a very short acting, cardioselective beta-adrenergic receptor antagonist.

 i.v. administration is used for rapid beta-receptor blockade in treatment of atrial fibrillation with high ventricular following rates.

 Antiarrhythmic effects are due mainly to beta-adrenergic receptor blockade. Normally, sympathetic drive results in increased in Ca²⁺ ,K⁺and Cl^- currents.

 Increased sympathetic tone also increases phase 4 depolarization (heart rate goes up), and increases DAD (delayed afterdepolarizations) and EAD (early afterdepolarization) mediated arrhythmias. These effects are blocked by beta-adrenergic receptor blockers.

Beta-adrenergic receptor blockers increase AV conduction time and increase AV nodal refractoriness, thereby helping to terminate nodal reentrant arrhythmias.