Patients with potentially lethal ventricular arrhythmias (VAs) represent a heterogenous group with frequent and high grade ventricular arrhythmias (including couplets and runs of nonsustained ventricular tachycardia), structural heart disease and decreased left ventricular function. This is a group at intermediate risk of sudden death, with risks varying from 10% to 38%. The electrical and mechanical risks of patients with potentially lethal VA is discussed in relation to their ability of promoting sudden death. The studies reviewing the impact of antiarrhythmic treatment on survival of patients with potentially lethal VA is discussed.