We present a patient with non-inducible atrial tachycardia (AT) after atriotomy for surgical repair of heart disease who underwent ablation successfully. Using a 3-D mapping system, we presumed the atriotomy site on the lateral right atrial wall by searching for linear double potentials (DP) during sinus/paced rhythm from the coronary sinus, but it was evaluated incompletely. We could verify the edges of the atriotomy scar precisely by pacing from close to the linear DP lesion and the opposite site. After ablation between the presumed atriotomy scar and the inferior vena cava and cavotricuspid isthmus, no AT recurred without anti-arrhythmic drugs.