ABSTRACT
Transesophageal echocardiography is a useful device to evaluate the posterior structure of heart with an advantage of enabling clearer images, as compared to transthoracic echocardiography. With intraoperative transesophageal echocardiography, we can reconfirm pre-diagnosed lesions, determine the success of the operation, and in particular, diagnose new lesions that are undetected in pre-operative evaluation. In the present case, undiagnosed patent ductus arteriosus was found on intraoperative transesophageal echocardiography during cardiopulmonary bypass. Subsequently, the patent ductus arteriosus was ligated successfully. With transesophageal echocardiography, we can diagnose the structural and functional abnormality of heart unidentified in the pre-operative evaluation. Also, transesophageal echocardiography can play the role of a rescuer to solve the problems that occur during cardiopulmonary bypass.