Emergency treatment of life-threatening arrhythmias is related to appreciation of their hemodynamic consequences. In all case, attention should be paid to treating the patient and not merely the electrical rhythm. Emergency cardioversion or defibrillation should be performed in tachyarrhythmias with associated significant end-organ hypoperfusion. Early drug therapy, stabilization, and referral for definitive therapy may be appropriate when tachyarrhythmias do not produce significant hemodynamic consequences. Asymptomatic bradycardia should not be treated emergently but referred for definitive care in those circumstances in which it is necessary. Bradycardia associated with end-organ hypoperfusion should be treated with trials of atropine, or isoproterenol, or emergency pacemaker insertion, and the stabilized patient referred to the cardiac procedure laboratory or cardiac care unit as appropriate. This same approach to bradyarrhythmias applies regardless of the anatomic and electrophysiologic etiology of the decreased heart rate. Attention to these few management principles clearly stresses the primary importance of the hemodynamic effects of any arrhythmia other than the arrhythmia itself.