Verapamil is an L-type calcium channel blocker of the phenylalkylamine class. It has been used in the treatment of hypertension, angina pectoris, cardiac arrhythmia, and most recently, cluster headaches. It is also an effective preventive medication for migraine. Verapamil has also been used as a vasodilator during cryopreservation of blood vessels. It is a class IV antiarrhythmic, more effective than digoxin in controlling ventricular rate, and was approved by the U.S. Food and Drug Administration (FDA) in 1981, some years after it was introduced in most Western countries.