The morphology of the first documented, the recurrent and the induced ventricular tachycardia were studied in 41 patients with an old myocardial infarction and documented sustained ventricular tachycardia. During a mean follow-up of 29 +/- 11 months recurrent ventricular tachycardia was present in 24 of 41 patients with the same morphology as the first ventricular tachycardia in nine (37.5%) and a different morphology in 15 patients (62.5%). Ventricular tachycardia with the same morphology as the spontaneous ventricular tachycardia were induced without significant differences between patients with recurrent events and those without. However, multiple morphologies of ventricular tachycardia (pleomorphism) were induced more frequently in patients with subsequent recurrence of ventricular tachycardia (off drugs: 9 of 13, 69%, on drugs: 14 of 23, 61%) than in patients without (off drugs: 4 of 10, 40%, on drugs: 2 of 11, 18%) (P less than 0.05). Pleomorphism of ventricular tachycardia induced during programmed stimulation identifies patients at a higher risk of subsequent recurrent events. Recurrent ventricular tachycardia has a different morphology than the first one in two thirds of patients.