In 3 patients with ischemic coronary disease or primary myocardiopathy who were unresponsive to conventional and experimental antiarrhythmia therapy, surgical treatment of intractable ventricular tachycardia was performed using epicardial, transmural, and endocardial mapping techniques. An experimental canine model of acute and chronic myocardial ischemia with recurrent ventricular tachycardia was developed to refine the mapping technique for clinical use. In patients and animals alike, atrial overdrive pause pacing, premature ventricular pacing, or both were used to bring outa repeatable pattern of tachycardia. Mapping techniques distinguished the irritable focus so that surgical excision of the site of earliest activation could be performed. In addition, the mapping techniques were used in the validation following excision. The limitations of epicardial mapping alone in locating all areas of premature focus are discussed, and the need for mapping in ventricular aneurysm is demonstrated.