A 11-month-old boy with a right ventricular diverticulum was reported. To our knowledge, this is the 18th case in the literature and the first case observed by two-dimensional echocardiography. Using our systematic two-dimensional echocardiographic approach, the three dimensional structure of this anomaly was reconstructed correctly. On the short-axis view of the ventricle, an abnormal septal echo was revealed in the right anterior region of the interventricular septum, forming an another cavity from the right ventricle, and was observed to have proper own motion by real-time two-dimensional echocardiography. From apical four chamber view, the abnormal cavity was detected on the right side of the small right ventricle. By contrast echocardiography, a contrast echo appears in the right ventricle and then in the abnormal cavity. The diagnosis was confirmed by cardiac catheterization, angiography and operation.