Esmolol (Brevibloc) is an intravenous, short-acting, titratable, cardioselective beta blocker with a very rapid onset and offset of action (t1/2 = 9.2 minutes). Esmolol-induced beta blockade can be maintained as long as infusion is continued. It exhibits neither intrinsic sympathomimetic activity nor significant membrane-stabilizing activity. It is rapidly metabolized by an esterase in the erythrocyte cytosol to an inactive acid metabolite. Its hemodynamic and electrophysiologic effects are similar to those of other beta blockers. Unlike the effects of other beta blockers, however, the effects of esmolol dissipate rapidly to baseline within 30 minutes after its discontinuation. Evidence obtained from clinical studies indicates that esmolol is effective and safe in reducing the ventricular rate in patients with supraventricular tachyarrhythmias, and in reducing the heart rate in patients with acute myocardial infarction and/or unstable angina. Esmolol has also been shown to be effective and safe in attenuating the tachycardia and hypertension seen during the intraoperative period. Data from postoperative patients indicate that esmolol is ideal as sole-agent therapy for the treatment of moderate postoperative hypertension associated with a hyperdynamic state. The short duration of action and titratability of esmolol make it an ideal drug for use in patients in whom the clinical need for beta blockade is limited in duration, and it offers additional safety in patients in whom beta blockade is beneficial; however, it might be precluded because of coexisting contraindications. To date, experience with esmolol in over 1200 patients has been gathered, and the adverse effect profile is basically similar to that reported here.