Blocks cardiac calcium channels in slow response tissues, such as the sinus and AV nodes.

In principle useful in treating AV reentrant tachyarrhythmias and in management of high ventricular rates secondary to atrial flutter or fibrillation, but rarely used due to the incidence of Torsades de Pointes, a serious ventricular arrhythmia.

Major adverse effect (i.v. administration) is hypotension. Heart block or sinus bradycardia can also occur.