Background : Radiofrequency catheter ablation(RFCA) plays increasingly important role in the treatment of idiopathic ventricular tachycardia(VT). But, there were few cases with idiopathic VT originated from aortomitral continuity in left ventricular outflow tract(LVOT). We report a case of RFCA for VT originated from aortomitral continuity by electroanatomical mapping system(CARTO). Case : A sixteen year-old woman with frequent palpitation admitted to our hospital. 3 years ago, she visited our hospital representing palpitation and dizziness. The electrocardiogram showed nonsustained ventricular tachycardia(NSVT) and RBBB morphology with inferior axis deviation. The echocardiography showed normal left ventricular function. We tried pace and activation mapping with RFCA by conventional method but failed. She took antiarrhythmic drugs(at first propafenone then changed to verapamil and bisoprolol), but complained recurrent palpitation. So we decided to retry RFCA. At this time, we tried activation mapping by electroanatomical mapping system. We performed activation mapping at right ventricle, aortic cusp and left ventricle during premature ventricular contraction(PVC). The earliest activation site was detected at aortomitral continuity in LVOT. The activation at this site preceded PVC on surface electrocardiogram by 38 seconds. After radiofrequency energy delivery for 479 seconds(11 times), the PVC disappeared. Thereafter, the patient had no more palpitation and the follow up holter monitoring showed normal sinus rhythm without PVC or NSVT.