S(-)-Propranolol HCl is a small molecule β-adrenergic receptor antagonist and the active isomer of (±)-Propranolol preparations. S(-)-Propranolol HCl blocks the binding of epinephrine, norepinephrine, and other endogenous catecholamines to the β-adrenergic receptor, impeding increases in cardiac flow velocity and general stimulation of the sympathetic nervous system signaled by association of these molecules to the β-adrenergic receptor. In addition to blockade of agonist binding, antagonism of the β-adrenergic receptor by S(-)-Propranolol HCl produces negative chronotropic and inotropic action, effectively dampening the force and rate of cardiac contraction. These negative chronotropic and inotropic effects correlate to a demonstrated suppression of adrenaline-induced cardiac arrhythmia by S(-)-Propranolol HCl. Suppression of β-adrenergic receptor activation by S(-)-Propranolol HCl has been widely exploited in counteracting situations sensitive to heightened cardiac activity including hypertension, angina pectoris, and cardiac ischemia.
