Scarring of the infarcted area after myocardial infarction is the most common cause of scar-related ventricular tachycardia. Other causes include right ventricular myocardial “dysplasia” (arrhythmogenic right ventricular cardiomyopathy), nodal disease involving the myocardium, and non-ischemic cardiomyopathy. The electrical signal encounters the dense scar tissue and is blocked from passing through, thus creating a relatively closed area of conduction. Although the scar area is mostly composed of fibrous connective tissue, it also contains scattered live cardiomyocytes. These live cardiomyocytes can form a pathway for electrical signal conduction through the scar tissue, but conduction is relatively slow. Thus, the relatively slow-conducting pathway in the scar tissue and the scar tissue surrounding the scar tissue, i.e., the border between scar tissue and normal tissue, can form a foldback loop. Because of the complexity of the conduction pathway formed by living cardiomyocytes within the scar tissue, which is zigzag or “labyrinthine” in shape, and the fact that different parts of the scar tissue border may form a foldback loop, the scar-related ventricular tachycardia foldback loop is very complex and highly variable. The scar-related ventricular tachycardia loop is complex and highly variable. However, regardless of the complexity of the loop, there are two commonalities that form the basis for the ablation of scar-associated ventricular tachycardia. One is that when the folding loop passes through the scar tissue, it always forms a narrow channel, which is like a narrow strait between two oceans, a critical position called the “isthmus” (the same concept of “isthmus” as in the previous discussion of atrial flutter ablation). Another point is that the electrical impulses return on the folding loop, passing through the isthmus in the scar tissue and the entire slow pathway, and exiting the scar tissue at a point called the exit. The location of the exit determines the shape of the ventricular waveform on the body ECG during ventricular tachycardia. The isthmus is often located in the vicinity of the exit. Ablation therapy of scar-associated ventricular tachycardia requires the use of a three-dimensional scaler system. The extent of the scar tissue is first determined in sinus rhythm, and the scar tissue is an area of low voltage because there is little excitable myocardial tissue. Since the scar tissue is a slow conduction region, it can also be determined with the help of pacing calibrations based on the time of electrical pulse delivery to excitation of the entire ventricle. Next, the outlet and isthmus are labeled. Marking of the exit is similar to that of idiopathic ventricular tachycardia and can be achieved by both excitation and pacing markers, but with less reliability than idiopathic ventricular tachycardia. The isthmus is marked mainly by the drag strip method. The isthmus is the target for ablation of scar-associated ventricular tachycardia, and ablation of the isthmus is usually performed at the onset of ventricular tachycardia. If the ventricular tachycardia can be terminated during ablation, this further validates that the ablation is performed at the exact site of the critical ventricular tachycardia folding loop. After successful ablation, ventricular stimulation needs to be repeated to induce ventricular tachycardia, and if ventricular tachycardia can no longer be induced, the treatment is more reliable. Scar-related ventricular tachycardia is variable in both the loop and the exit, a feature that makes ablation treatment difficult and affects the outcome of ablation therapy. At one year after surgery, approximately 40% of patients have recurrence of ventricular tachycardia. The complication rate of the procedure is at the level of 10%, and the procedure-related mortality rate is 1 to 3%. Because of the high risk of scar-related ventricular tachycardia, the consequences are often severe, and because ablation therapy does not have the same success rate as idiopathic ventricular tachycardia or paroxysmal supraventricular tachycardia, ICD implantation should be considered when an ICD is indicated. Ablation therapy for scar-related ventricular tachycardia is currently used mainly in cases of frequent episodes of ventricular tachycardia and frequent ICD discharges after ICD implantation, and it cannot replace ICD implantation therapy. Catheter ablation therapy should only be the treatment of choice in cases of restless ventricular tachycardia (which is a contraindication to ICD implantation).