We investigated the clinical and electrophysiological features of monomorphic ventricular tachycardia (MVT) with different initiation patterns in patients with implantable cardioverter defibrillator to assess whether there is a relationship between the initiation patterns of sustained MVT and clinical characteristics, and the efficacy of antiarrhythmic and electrical therapy. Fifty-five stored IECGs in twenty-two patients with MVT were evaluated. All MVT episodes were classified as initiating with ventricular premature beats (non-sudden onset MVT) or without ventricular ectopy preceding tachycardia (sudden onset MVT). Non-sudden onset MVT was characterized by shorter tachycardia cycle length (CL) and required higher shock energy for termination. Sudden onset MVT was precipitated by shortening of the sinus CL before tachycardia and was more common with relatively better preserved systolic function. (C) 2003 Elsevier Ireland Ltd. All rights reserved.