Atrial tachycardias (AT) are common cardiac arrhythmia disorder for congenital heart disease (CHD). The anatomic substrate that surgical suture lines, scar tissue, or prosthetic material may cause pre-existing atrial conduction abnormalities which leads to the underlying mechanism of reentrant ATs. Radiofrequency Catheter ablation (RFCA) is used in the treatment of atrial tachycardia in CHD patients. However venous system abnormalities may complicate the procedure. We report that ablation of a case with atrial tachycardia with challenging anatomy (persistent left superior vena cava draining into the left atrium, coronary sinus agenesis, inferior vena cava (IVC) agenesis, azygos system drained to the superior vena cava, and repaired ventricular septal defect). This case report discusses the key points of access to cardiac chambers and mapping in very rare challenging anatomy.