Introduction Atrial tachycardias are wide spectrum of arrythmias with both focal and macro reentrant etiology. Among them, especially in patients with corrected congenital heart defects, complex arrythmias such as dual-loop MRAT may develop. In such cases successful ablation is always challenging. Methods and Results A 31 year old female with known genetic disorder, post ASD II and VSD corrective surgery was admitted to the cardiology ward due to persistent atrial flutter and a possible tachycardiomyopathy for arrhythmia substrate ablation. During the procedure, difficulties with RA catheterization were observed with IVC anomaly, draining into the RA through azygos vein and SVC. Activation and potential maps were obtained during the tachycardia, revealing a dual-loop reentry around the tricuspid annulus and the superior part of crista terminalis. RF applications were delivered in the expected reentry isthmus on crista terminalis and in the “cavo-tricuspid isthmus”, however a persistent CTI block was not achieved. CT was later performed, revealing multiple venous anomalies, confirming an interrupted IVC draining through the azygos and SVC into the RA with an atrial part of IVC developing only from hepatic veins and a coronary sinus draining into the left atrium. The patient spontaneously converted into sinus rhythm on the next day after the procedure and was referred for a redo procedure at a later term. Results These findings underscore that ablation of complex arrhythmias such as dual loop RA MRAT especially in patients with known genetic disorders and congenital heart is technically demanding and should be performed using advanced technology, under general anesthesia to enhance catheter stability, patient safety, and overall procedural success.