We performed epicardial and endocardial mapping in 11 patients with ventricular aneurysms; six had chronic, recurrent ventricular tachycardia and five had no ventricular arrhythmias more severe than isolated ventricular premature complexes. Forty to 66 epicardial and 16-40 endocardial points were recorded during stable sinus rhythm in each patient. Local electrograms were evaluated as to timing and presence of fragmentation (duration greater than 50 msec, amplitude less than 1 mV, absence of discrete intrinsicoid deflection). Activation of the epicardial surface of the aneurysm was abnormal in all patients, and extended beyond completion of the QRS in three patients in the arrhythmia group and two in the nonarrhythmia group (NS). Activation of the epicardial border zone was normal in all patients. Electrograms from the endocardial surface of the aneurysm were abnormally fragmented in all patients and the mean duration of activation was not different between patients with and without arrhythmias (85.5 +/- 14.1 vs 96.2 +/- 13.8 msec, NS). However, in patients with ventricular tachycardia, electrograms from 33-58.3% (mean 45.5 +/- 8.8%) of the endocardial border zone showed fragmentation, compared with 0-16.7% (mean 4.9 +/- 7.4%) of the endocardial border zone in patients without arrhythmias (p less than 0.05). Fragmentation was always along the septal border of the aneurysm. The mean duration of the most prolonged endocardial border zone electrogram was 97.5 +/- 17.0 msec in ventricular tachycardia patients and 67.0 +/- 27.1 msec in patients without arrhythmia (p less than 0.05). Five of six ventricular tachycardia patients had electrical activity in the endocardial border zone extending beyond the end of the QRS, compared with one of five patients without ventricular tachycardia (p less than 0.05). We conclude that fragmented electrical activity is present in all patients with ventricular aneurysms, but the extent and severity of fragmentation in the endocardial border zone is greatest in patients with recurrent ventricular tachycardia.