A long vertical vestibule with a diverticulum-like morphology of cavotricuspid isthmus (CTI) was demonstrated by right atrial angiogram in a 47-year-old male patient in whom his typical atrial flutter was difficult to be ablated. Compatible with the right atrial angiography, the diverticulum-like CTI with a long vertical vestibule, pouch-like recess, and a long transverse posterior component was also demonstrated on volume-rendering reconstruction computed tomography and the virtual endoscopy showed prominent trabeculation inside the diverticulum-like part of CTI. The bidirectional CTI conduction block was successfully achieved after ablating along the CTI guided by the right atrial angiography.