Recently, real-time 3-dimensional transesophageal echocardiography (3D-TEE) was introduced to allow online acquisition, rendering, and provision of accurate information on cardiac structures. We report our initial experience of this modality. The 1st patient had mitral valve insufficiency; mitral valve prolapse of the P2 segment was clearly visualized by preoperative 3D-TEE. The 2nd patient had severe aortic stenosis, in whom 3D-TEE demonstrated fusion of the non- and right-coronary cusps. The 3rd patient had ventricular septal defect (perimembranous type), and 3D-TEE precisely demonstrated the size, shape, and location of the defect. The diagnoses were confirmed intraoperatively in all the patients. In conclusion, real-time 3D-TEE was useful for assessing the anatomical features of heart structures, enabling us to perform safer operations.