Medically intractable ventricular arrhythmias are a common problem with serious consequences. Direct myocardial surgery aimed at ablation or isolation of the arrhythmic circuit, localized by cardiac mapping, offers an alternative treatment that can eradicate the tachycardia. The success of various surgical approaches depends on an accurate assessment of mechanism, concise localization of the arrhythmic circuit by electrophysiologic means and proper selection of the patients most likely to benefit from the procedure. Most forms of ventricular arrhythmias are due to reentry and are typically associated with an abnormal substrate such as infarction, fibrosis or ventricular aneurysm. However, superficially (epicardially) the activation sequence may appear to resemble an abnormal automatic focus tachycardia. Confirmation of the reentrant nature of the tachycardia depends on demonstrating delayed activation in a region close to, or connected to, the site of origin. This frequently requires multiple intramural electrode recordings or endocardial mapping, or both. In the past, the rationale for surgery or for the specific surgical approach has not always been explicit. It was not always clear why a particular surgical approach terminated or failed to terminate the arrhythmia. In some patients the basis of control of the tachycardia could not be explained and the effect was partly accidental. Successful surgical control of ventricular arrhythmias depends on (1) a more precise clarification of mechanism, specifically a more comprehensive definition of the reentrant structure in the individual patient; (2) improved techniques for cardiac mapping, including simultaneous recording of potentials from multiple areas, aimed intramural-endocardial recordings and immediate (computerized) display of the activation map data; and (3) improved surgical techniques based on (1) and accurately guided by (2).