The diagnosis, management, and surgical decision-making in children and adults with congenital heart disease are largely based on echocardiography findings. A recent development in cardiac imaging is fusion of different imaging modalities. Our objective was to evaluate the feasibility of computed tomography (CT) and 3D transthoracic echocardiography (TTE) fusion in children and adults with congenital heart disease. We prospectively included 13 patients with congenital heart disease and 1 patient with a normal heart who underwent both CT and 3D TTE as part of their usual follow-up at our center; median age was 9.5 years [2.7-15.7], 57% were male, and median body surface area was 0.9 m2 [0.6-1.7]. Congenital heart disease was classified as simple ( n = 4, 29%), moderate ( n = 4, 29%), or complex ( n = 6, 42%). We described the steps required to complete the fusion process (alignment, landmarks, and superimposition), navigation, and image evaluation. 3D TTE-CT fusion was successful in all patients. Median total time to complete the fusion process was 735 seconds [628-1163], with no significant difference according to the degree of complexity of the cardiopathy. Landmarks were significantly modified in complex congenital heart disease ( Fig. 1 ). We established the feasibility and accuracy of 3D TTE-CT fusion in a population of children and adults with a variety of congenital heart diseases. The simultaneous visualization of many intracardiac structures may help to understand the anatomical features of congenital heart disease without limitations regarding age, weight, or complexity of the congenital defects.