Sudden cardiac death continues to pose a major public health problem in the United States. The underlying cause in the vast majority of patients is arteriosclerotic heart disease, and the pathophysiologic mechanisms are ventricular tachycardia and ventricular fibrillation. In patients identified to be at great risk for sudden cardiac death, both noninvasive and invasive techniques are available to help guide antiarrhythmic therapy. When arrhythmias occur frequently, noninvasive techniques may be adequate to allow sequential pharmacologic testing until an effective regimen can be defined. However, in patients whose frequency of arrhythmia at rest is low, provocative techniques are required. In patients for whom a successful pharmacologic regimen is defined, the outlook is good and the chance of sudden cardiac death is considerably decreased.