Congenital anomalous origin of coronary artery is a rare cardiovascular malformation and the most common anomaly is the left circumflex (LCX) arising from the right sinus of Valsalva (RSV). Other forms include both coronary arteries from RSV, the left anterior descending coronary artery from RSV, and a single coronary artery from the left sinus of Valsalva. Despite being rare, anomalous origin of left main coronary artery (LMCA) from RSV carries a high risk of sudden cardiac death. Here, we report a case of 13-year-old boy with chest pain and acute extensive anterior ST-segment elevation myocardial infarction (STEMI) who was initially diagnosed as acute myocarditis in the emergency department. A bedside echocardiogram showed severe global hypokinesia of left ventricle (LV) and normal right ventricle (RV) function. Coronary computed tomography angiography (CCTA) examination showed LMCA originated from the RSV. The patient underwent coronary artery bypass grafting surgery and was discharged without complications. A timely correct diagnosis of an anomalous coronary artery is critical in symptomatic patients, CCTA plays an important role in clinical decision making.