Transesophageal echocardiography (TEE) provides real-time information on both morphology and hemodynamics without radiation exposure or contrast media, interruption of surgical procedures, or need for transferring the patient to other division, and thus can be used as intraoperative monitoring as well as diagnostic imaging. TEE is helpful for confirming the adequacy of routine surgical procedures, ruling out an occurrence of unexpected adverse events, or even navigating the manipulations of cannulae and catheters. In mitral valve repair, TEE assessment is essential for secure success and making a decision of 2nd pump run with a strategy for re-repair. In acute aortic dissection, TEE is often the only information source for making treatment strategy or detecting unexpected events. TEE provides unique information on properties of tissues, thrombus, or blood, which cannot be identified even with fluoroscopy, thus TEE is to be used efficiently in the hybrid operating room (OR). In thoracic surgery, TEE is helpful for assessing an invasion of tumor to the adjacent structures including the aorta or heart. With all these capabilities of TEE, it should be fully utilized to optimize the outcomes of thoracic and cardiovascular surgeries.