Ventricular tachycardias(VTs) usually complicate iscemic heart disease. Cardiomyopathy or other organic heart disease and are aften associated with sudden cardiac death. Ventricular tachycardias with no apparent cardiac abnormalities, however, have been known to have different clinical features comprising a unique clinical entity among other tachycardias. Eleven patients(7men, 4 women) were investigated on their clinical features, electrophysiologic studies and late potentials. 1) The mean age at diagnosis was 23.4+/-6.5 years and the predominating clincal features were palpitation, syncope or congestive heart failure. No death occured over a mean follow up period of 29.2+/-26.5 months. 2) The resting ECGs were within normal limits in 8 patients and showed nonspecific ST-T changes in 3 patients. 3) Ventricular pacing induced sustained ventricular tachycardias in 7 patients and nonsustained VT in 1 aptient. Atrial pacing could provoke sustained VTs in 3 patients. 4) His bundle electrograms(HBE) were obtained in 7 patients during tachycardial. The HV intervals of the induced VTs distributed between 0 to -25msec in 5 patients and there was no definite His potentials in two patients. 5) The coupling interval of premature stimuli and the echo interval(the interval from the stimulus to the initiation of resulting VT) showed inverse relationship in 5 cases. No direct relationship was observed. 6) The termination mode, observed in 7 patients, showed delayed ternmination in 2 patients. 7) Late potentials(LPs) were pisitive in three patients but there was no significant statistical difference between LPs in normal control and those with idiopathic sustained left VTs. 8) Verapamil terminated VTs in 8 patients and slowed the rate of tachycardial in 1 patient. In conclusion, idiopathic sustained left ventricular tachycardias occur in younger age group and have more favorable prognosis. The findings of EPS and LPs suggest microreentry or triggered activity as their basic mechanism and verapamil can be used effectively for their termination.