How to use real-time three-dimensional (3D) echocardiography for diagnosis and treatment of congenital heart diseases? To obtain morphological details of complicated intracardiac structure is one of the most effective usages, when planning for cardiac surgery, such as an intracardiac rerouting through ventricular septal defect in patients with double-outlet right ventricle, valvuloplasty for complicated atrioventricular valve regurgitation, or release for intracardiac stenotic lesions. Especially, intraoperative transpericardial 3D echocardiography performed by putting the 3D probe on the pericardium directly enables us to get the good quality images with a high S/N ratio in pediatric patients less than 20 kg of body weight, for whom transesophageal 3D echocardiography cannot be applied. This approach also enables both cardiovascular surgeons and cardiologists to share the "surgeon's view" in the operating room quickly. Moreover, transesophageal 3D echocardiography is also useful for the decision for the indication of catheter intervention and monitoring the procedure of the percutaneous closure of atrial septal defect, as well as to diagnose the abnormal morphology and guide the intracardiac surgery in children more than 20 kg of body weight with congenital heart disease.