ANOMALOUS origin of left coronary artery from pulmonary artery (ALCAPA) is a rare coronary artery anomaly, with an incidence of 1 in 300,000 live births. If left untreated, mortality is up to 90% in the first year of life because of progressive left ventricular (LV) dysfunction. 1 McKenzie I, Zestos MM, Stayer AS, et al. Anesthesia for miscellaneous cardiac lesions. In Andropoulos DB, Stayer AS, Mossad EB, et al (eds). Anesthesia for congenital heart disease, ed 3. Hoboken, NJ, John Wiley & Sons, pp 598-635. Google Scholar Therefore, early diagnosis and prompt surgical intervention are necessary in all patients when this lesion is identified. The commonly performed surgery in these patients is direct reimplantation of the anomalous left coronary artery (LCA) into the aortic root using cardiopulmonary bypass (CPB). Transesophageal echocardiography (TEE) is performed routinely in ALCAPA patients during the pre- and post-CPB periods for the assessment of coronary artery origins and flow patterns, LV function, and mitral regurgitation (MR). 2 Frommelt PC Congenital coronary artery anomalies. in: Pierre CW Wanda CM-H Transesophageal echocardiography for congenital heart disease. Springer, London, United Kingdom2014: 371-382 Crossref Scopus (2) Google Scholar Although thrombus formation during CPB despite full heparinization is reported in adults, 3 Kim SH Ryu JS Kim TY et al. Abrupt formation of intracardiac thrombus during cardiopulmonary bypass with full heparinization-a case report. Korean J Anesthesiol. 2012; 62: 175-178 Crossref PubMed Scopus (8) Google Scholar LV thrombus formation during CPB in surgery for ALCAPA is not reported in the literature. Herein, the authors report a case in which the intraoperative TEE detected a free-floating LV thrombus in the immediate post-CPB period during the surgical repair of ALCAPA and in which the clots were removed by reinstitution of CPB.