Using transesophageal echocardiography in the operating room has increased dramatically in recent decades. This technique is now accepted as a routine tool with established recommendations and guidelines for continuous quality improvement in perioperative care. However, It is important to distinguish between advanced perioperative transesophageal echocardiography (PO-TEE) and basic PO-TEE. The main goal of basic PO-TEE and basic PO-TEE. The main goal of basic PO-TEE is cardiac monitoring and finding the cause of instability in unstable surgical patients. The advanced PO-TEE is the standard tool for monitoring and care of the entire spectrum of cardiac surgery procedures ranging from simple coronary revascularization to complex repair. The goals of advanced PO-TEE in the cardiac operating room are: 1. Confirming the preoperative diagnosis, 2. Detect new and unexpected pathology 3. Guide surgical team in their treatment plan and hemodynamic management 4. Assess the results of the surgical procedure. 5. Diagnose the etiology of hemodynamic instability. This chapter covers the role of perioperative transesophageal echocardiography (PO-TEE) in the care and treatment of patients undergoing cardiac surgery.