Coronary artery aneurysm (CAA) is a rare cardiac anomaly with a reported incidence of 0.3-4.9% of patients who undergo coronary angiography. The term is used when the coronary artery diameter exceeds more than 50% or 1.5 times the reference diameter. It can be congenital or acquired. The commonest acquired cause in an adult is atherosclerosis and in a child is Kawasaki's disease. The commonest culprit vessel is the Right Coronary Artery (RCA), followed by Left Circumflex (LCx) and Left Anterior Descending (LAD). Left main coronary aneurysms are extremely rare in clinical practice. Coronary angiography is the gold standard procedure, both for diagnosis and treatment. We report a 49-year-old male who presented with anterior wall ST-Elevation Myocardial Infarction (STEMI). The initial angiography showed LAD stent thrombosis, but when the second angiography was done, there was spontaneous recanalization of the LAD. Coronary angiography was performed at our hospital, which revealed a long left main coronary artery aneurysm measuring 9.8 mm-maximum diameter. This was treated with a size 5 × 24 mm Begraft coronary stent.