Focal atrial tachycardias (ATs) can originate anywhere in either atria and their appendages and the aortic root.However, to our knowledge, there has been less report of an AT originated from LCC.Patient Characteristics and Electrophysiological Study A 35-year-old woman with paroxysmal palpitations and refractory to treatment with antiarrhythmic drugs (AADs) referred to our department.The twelve-lead ECG recorded during the episodes showed the P-wave morphology.A sustained atrial tachycardia (AT) with 3∶2 atrioventricular conduction was observed throughout EP study by intravenous isoproterenol infusion, and EnSite Array (EA) simultaneously reconstructing three-dimensional (3D) images of right atrium (RA) demonstrated that the AT originated sites were clustered at the right atrial septum which was reconfirmed with NavX system.After intensive activation mapping at this region, the earliest atrial activation site was para-His bundle (HB) merely preceded of the P wave onset in the surface ECG by 22 ms.Considering AT possibly to arise from the left atrium (LA), mapping in the aortic cusp was performed to identify a potential focus of the tachycardia after transseptal puncture failed to assess the LA.The aortography demonstrated the earlist atrial potential recorded inside the left coronary cusp (LCC) preceded the P-wave onset in the surface ECG by 41 ms,and earlier than that of the noncoronary cusp (NCC) and HB.The radiofrequency energy with power 40 W and maximum temperature of 55 ℃ delivered at this site terminated the AT in 5 seconds, and without AT spontaneous or inducible by isoproterenol infusion.No recurrence was observed with 24h Holter recordings during a three-month follow-up without any antiarrhythmic drugs.