There is extensive experimental and clinical experience concerning the antiarrhythmic potency of DL-sotalol, a beta-adrenergic antagonist that lengthens the cardiac action potential duration. More recently, its dextrorotatory isomer, D-sotalol, has been evaluated in experimental studies and preliminary clinical trials. Whereas the isomer is almost free of beta-blocking activity, both experimental and clinical data demonstrate that potent class III activity of D-sotalol. Further investigations, particularly in patients with life-threatening arrhythmias, are needed to delineate the clinical usefulness of this compound.