Esmolol is a beta-adrenergic receptor antagonist with a relatively specific affinity for beta 1 adrenergic receptors. Its mechanism of action is therefore largely cardioselective and only high doses block beta 2 adrenergic receptors. The pharmacologic features of the drug give it rapid onset of beta-blocking action (distribution half-life = 2 minutes) and a short duration of action due to rapid clearance (clearance half-life = 9 minutes). The rapid metabolism of esmolol allows its beta-blocking activity to be lowered rapidly by changing the rate of infusion and obtaining rapid reversibility of effect in the minutes following interruption of the infusion. The esmolol dose is therefore manageable and individual adjustments can be made in function of a patient's clinical status. Such properties mean that esmolol is indicated for short-term treatment of hypertension and tachycardia during the perioperative period and in clinical situations that require easy unblocking of beta receptors. Hypertension and bradycardia are the most frequent complications associated with the administration of esmolol, such that blood pressure, heart rate and electrocardiographic data must be monitored.