Carbon monoxide (CO) poisoning is the most common cause of death and injury among all poisonings. Myocardial injury is detected in one-third of CO poisonings. In this Case Report, a previously healthy 41-year-old man was referred for CO poisoning. The initial electrocardiogram (ECG) showed 1 mm ST segment elevation in leads DII, DIII, and aVF. As the patient did not describe chest pain and had no cardiac symptoms, ECG was repeated 10 minutes later and it was seen that ST segment elevation disappeared. As the patient had a transient ST segment elevation and elevated high-sensitive Tn-T (HsTn-T), the patient was transferred to the coronary angiography laboratory. The patient's left coronary system was normal, but a thrombus image narrowing the lumen by approximately 60% was observed in the right coronary artery. Intravenous tirofiban was administered for 48 hours. Control coronary angiography showed continuing thrombus formation and a bare metal stent was successfully implanted. This is the first reported case with transient ST segment elevation associated with acute coronary thrombus caused by CO poisoning. It may be recommended that patients with CO poisoning should be followed-up with a 12-lead ECG monitor or 24-hour ECG Holter monitoring, even if they show no cardiac symptoms and echocardiography shows no wall motion abnormality. Early coronary angiography upon detection of such dynamic ECG changes in these recordings as ST segment elevation can reduce the risk of myocardial infarction (MI) and mortality in these patients.