Abstract : Tetralogy of Fallot (TOF) remains the most common complex cyanotic congenital heart defect. One of the main adult congenital heart disease (ACHD) concern is the late risk of arrhythmias. ACHD with cyanosis prone to induced Atrial Tachycardia (AT). We present a rare case of long-term adult survivor with uncorrected TOF who developed incessant AT induced hypoxic spell. A 34 years old women with uncorrected TOF was admitted to emergency department with chief complaint of palpitation. The electrocardiography showed atrial tachycardia 2:1. The patient refractory to many pharmacological treatments. Patient were given amiodarone, diltiazem and underwent electrical cardioversion. The catheter ablation was planned but the patient died due to hypoxic spell. Adults with cyanosis congenital heart disease has risk of AT, which patients with cyanosis have prevalence 31% vs 7.9% compared with noncyanosis. Most atrial tachycardias in patients with CHD involved a macroreentrant circuit within abnormal atrial muscle. Treatment options for AT with haemodynamically stable include vagal manoeuvre, adenosine and AV nodal-blocking agents such as ß-blocker or calcium channel blockers and synchronized cardioversion for haemodynamically instability. Catheter ablation is the treatment of choice for incessant AT. In this case, patient refractory to treatments and became incessant AT. Hypoxic spells can be induced by an atrial tachycardia. In TOF patient, with its basic arterial desaturation, diminished cerebral flow, lowered aortic and ventricular pressures, probably additional right to left shunt shunting of desaturated blood at ventricular level with rise in pulmonary vascular resistance, are superimposed during arrhythmia event. This condition maybe explained why the patient had an episode of desaturation. Arrhythmias in TOF were common. Cyanosis become risk factor for leading into arrhythmias and arrhythmias also induced cyanosis, creating a vicious circle. Acute therapy and catheter ablation were remaining golden therapy for termination of arrythmias