Carbon monoxide intoxication is one of the most common types of poisoning and it is the leading cause of death by poisoning in the world. We report a carbon monoxide intoxication case presenting with atrial fibrillation on 17 years old healthy boy. 17 years old boy admitted to emergency service after exposuring carbon monoxide gas approximately 3 hours. His first electrocardiography (ECG) showed atrial fibrillation with rapidly ventricular response. After oxygen supply sinus rhythm was achieved spontaneously. Emergency physicians should be aware of the clinical presentation of carbon monooxide intoxication. Every patient that arrived emergency service with acute or chronically carbon monoxide poisoning should undergo cardiovascular investigation, including ECG and measurement of cardiac enzymes.