Verapamil hydrochloride injection, USP is indicated for the following: Rapid conversion to sinus rhythm of paroxysmal supraventricular tachycardias, including those associated with accessory bypass tracts (Wolff-Parkinson-White and Lown-Ganong- Levine syndromes). When clinically advisable, appropriate vagal maneuvers should be attempted prior to verapamil hydrochloride administration. Temporary control of rapid ventricular rate in atrial flutter or atrial fibrillation except when the atrial flutter and/or atrial fibrillation are associated with accessory bypass tracts (Wolff-Parkinson-White and Lown-Ganong-Levine syndromes). In controlled studies in the United States, about 60% of patients with supraventricular tachycardia converted to normal sinus rhythm within 10 minutes after intravenous verapamil hydrochloride. Uncontrolled studies reported in the world literature describe a conversion rate of about 80%. About 70% of patients with atrial flutter and/or fibrillation with a faster ventricular rate respond with a decrease in ventricular rate of at least 20%. Conversion of atrial flutter or fibrillation to sinus rhythm is uncommon after verapamil hydrochloride and may reflect the spontaneous conversion rate, since the conversion rate after placebo was similar. Slowing of the ventricular rate in patients with atrial fibrillation/flutter lasts 30 to 60 minutes after a single injection. Because a small fraction of patients treated with verapamil hydrochloride respond with life-threatening adverse responses , the initial use of verapamil hydrochloride injection should, if possible, be in a treatment setting with monitoring and resuscitation facilities, including D.C.-cardioversion capability. As familiarity with the patient's response is gained, use in an office setting may be acceptable. Cardioversion has been used safely and effectively after verapamil hydrochloride injection.