Endocardial lesions created by radiofrequency catheter ablation are relatively small and focal. The application of radiofrequency ablation to patients with structural heart disease and ventricular tachycardia is quite limited because the substrate for these tachycardias is often diffuse or difficult to localize. In contrast, idiopathic ventricular tachycardia often originates from a discrete focus and can usually be ablated using radiofrequency energy. The wider applicability of ablation therapy for ventricular tachycardia will depend on improvements in mapping techniques and the ability to create larger areas of injury in patients with coronary artery disease and ventricular tachycardia.