Astra Hässle (now Hässle Läkemedel, a subsidiary of AstraZeneca) of Sweden was developing an IV formulation of almokalant for use in the treatment of atrial arrhythmias. Almokalant is a selective blocker of the delayed outward K+ current. Almokalant exhibited properties of a selective class III antiarrhythmic agent, devoid of β-blocking activity, in vitro and in vivo, in animals and humans. In humans, prolongation of the refractoriness of the atria and ventricles has been demonstrated, as well as a prolongation of the ventricular repolarization. A moderate antiarrhythmic efficacy has been disclosed in studies in patients with supraventricular reciprocating tachycardias, with atrial fibrillation and with premature ventricular contractions. Almokalant also has proarrhythmic potential and thedevelopment of almokalant was discontinued due to induction of Torsade de Pointes, which occurred in some susceptible patients during the clinical trials.