Transesophageal echocardiography (TEE) and epicardial echocardiography have changed the treatment option for intraoperative period of cardiac surgery and helped cardiac surgeons to understand the pathophysiology of heart prior to the surgery. They have also resulted in a better outcome after the cardiac surgery. TEE has an advantage of having direct assessment of cardiac structure without having interference in the surgical field. This chapter covers the important role in modern cardiac surgery, important role in modern noncardiac surgery, echocardiographic technique, important preparation of perioperative echocardiography, valvular heart disease in operation theater, assessment of the patient for mitral valve repair, aortic valve pathology and evaluation for repair in OT, transesophageal echocardiography during major aortic surgery and reconstruction, left ventricular function and wall motion abnormalities intraoperatively, errors and artifacts in assessment in OT with ascending aorta, pathology of aorta and role of transesophageal echocardiography in operation theater for acute aortic syndrome, and epicardial probe preparation.