Aneurysm of the left sinus of Valsalva is an extremely rare entity. It may be asymptomatic and incidentally discovered, or may be symptomatic and manifest acutely with compression of adjacent cardiac structures. Encasement of the left main coronary artery by such an aneurysm is a recognized but infrequent complication that can lead to severe coronary insufficiency. Surgical decompression of the left main coronary artery is the standard treatment for such conditions. We describe a patient presenting with extrinsic compression of the left main coronary artery by a large unruptured aneurysm of the left sinus of Valsalva occurring 4 months after unsuccessful surgical repair. Since reoperation was considered high-risk for the patient, successful fractional flow reserve- and intravascular ultrasound-guided percutaneous treatment of the left main coronary artery was performed with implantation of one bare-metal stent.