Spontaneous Polymorphism (SP) is present when at least two episodes of Sustained Ventricular Tachycardia (SVT) occur spontaneously in the same patient (pt) with different bundle branch block pattern or with shifting of QRS axis by greater than or equal to 90 in the various episodes. We undertook this study in order to investigate the clinical significance of SP in SVT as well as therapeutic and prognostic implications. MATERIAL AND METHODS. From our global pts populations we chose those with SVT in chronic ischemic heart disease (CIHD) with previous myocardial infarction (PMI), they had to be already studied by electrophysiologic technique (EES). The pts were divided into two groups (Gr.): Gr. I: 13 SP pts (12 M, 1 F, mean age 57.5 +/- 13; mean follow-up 19.2 +/- 11 months); Gr. II: 15 no SP pts (14 M, 1 F, mean age 60 +/- 10; mean follow-up 9.9 +/- 13 months). RESULTS The two Gr. are comparable in terms of symptoms, exercise tolerance, infarct site, intraventricular conduction disturbances (61.5% and 66.6% respectively), ventricular wells kinetics (38.4% and 26.6% respectively) and time interval between acute myocardial infarction the first episode of SVT (7.58 +/- 6.02 and 8.27 +/- 6.57 years respectively). 8 of the 10 alive Gr. I pts have been treated with Amiodarone (A) (2800-4200 mg/wk). All 9 alive Gr. II pts are on A (1400-4200 mg/wk). A serum level in 7 Gr. I pts was 1.7 +/- 0.65 mcg/ml and 1.61 +/- 0.67 in 5 Gr. II pts. 3/13 Gr. I pts died: 2 for sudden death (15.3%), 6/15 Gr. II pts died: 4 suffered sudden death (26.6%).(ABSTRACT TRUNCATED AT 250 WORDS)