In this chapter, the role of 3D TEE in the operating room in different cardiac pathologies is discussed. In each case, examples of pre- and postoperative images have been provided and to present echo images of every case with related surgical cases for correlation. 3D TEE creates a common language between cardiologist, cardiac surgeon, and interventionist in the operating room and in the cath laboratory for decision making. Like any other new technique, 3D echo has its own limitations and needs further technical improvement. Aortic valve disease, cardiac masses, limitations of 3D TEE, mitral valve disease, native valve endocarditis , prosthetic valve dysfunction are tricuspid valve disease are described in details. More than 224 comprehensive and self-explanatory images are included in this chapter. And 78 references are given at the end of the chapter to facilitate further reading.