This chapter deals with the management of arrhythmias that occur as a complication of other cardiac and medical disorders. Broad-complex tachyarrhythmias usually arise from the ventricles, although some ventricular tachyarrhythmias arise high in the bundle of His and can be relatively narrow. The onset of an arrhythmia is often associated with problems such as heart failure, pulmonary infection or embolism, thyroid disturbance, hypoxia, electrolyte imbalance or drug administration. The appearance of the surface electrocardiogram and the type of arrhythmias that occur depend on the precise anatomy and conduction characteristics of the accessory pathway. Antiarrhythmic drugs that stabilize atrial electrical activity may terminate the arrhythmia. The occurrence of monomorphic ventricular tachycardia with a left bundle and right axis configuration in a patient with a normal heart indicates that the arrhythmia is arising from the right ventricular outflow tract. Patients who present with symptomatic bradyarrhythmias due to chronic conduction system disease may require short-term support to maintain an adequate heart rate.