Objectives We sought to determine whether atrial tachycardia arising adjacent to the noncoronary aortic sinus (NCAS—AT)has distinctive atrial activation patterns in relation to targeted anatomic imaging.Background The knowledge of atrial activation patterns of the NCAS—AT and its anatomic basis is very limited.Methods Three—dimensional electroanatomic mapping was performed during NCAS—AT in 13 patients and during sequentially pacing from the noncoronary aortic sinus (NCAS) and the paraHisian atrial area in 15 reference patients.The spatial relationship between the NCAS and the contiguous atria was studied in another 25 reference patients using computed tomography and in 12 human hearts using gross and microscopic anatomic examination.