A prospective survey was conducted of the indications for and complications of 153 temporary transvenous cardiac pacing lead insertions in 148 patients. Pacing for bradyarrhythmias or potential bradyarrhythmias (Group I) accounted for 105 insertions, wide complex tachycardia (Group II) 17, and narrow complex tachycardia (Group III) 31 pacing electrode insertions respectively. The infraclavicular subclavian vein approach was used in 73%. The median insertion time was 20 minutes. Group I: 77% were undertaken because of severe symptoms. On 64 occasions (61%) the patient had complete heart block or ventricular asystole. Group II: The lead was inserted to treat and often assist in the diagnosis of the wide complex tachycardia. Ventricular 'burst' pacing reverted ventricular tachycardia in 13 (76%). Group III: Rapid atrial 'burst' pacing was used to treat supraventricular tachyarrhythmias (paroxysmal supraventricular tachycardia and atrial flutter) resistant to medical therapy. Pacing was successful in reverting 28 (90%). A complication occurred in 27 (18%) of 153 lead insertions, 11 (7%) were serious. No complication resulted in the death of a patient. Temporary transvenous pacing is safe and effective for the treatment of bradyarrhythmias and certain tachyarrhythmias.