Background: Accurate visualization of cardiac valves and lesions by three-dimensional (3D) echocardiography is integral for optimal guidance of structural procedures and appropriate selection of closure devices. A new 3D rendering tool known as transillumination (TI), which integrates a virtual light source into the data set, was recently reported to effectively enhance depth perception and orifice definition. We hypothesized that adding the ability to adjust transparency to this tool would result in improved visualization and delineation of anatomy and pathology and improved localization of regurgitant jets compared with TI without transparency and standard 3D rendering.Methods: We prospectively studied 30 patients with a spectrum of structural heart disease who underwent 3D transesophageal imaging (EPIQ system, Philips) with standard acquisition and TI with and without the transparency feature. Six experienced cardiologists and sonographers were shown randomized images of all three display types in a blinded fashion. Each image was scored independently by all experts using a Likert scale from 1 to 5, while assessing each of the following aspects: (1) ability to recognize anatomy, (2) ability to identify pathology, including regurgitant jet origin, (3) depth perception, and (4) quality of border delineation.Results: TI images with transparency were successfully obtained in all cases. All experts perceived an incremental value of the transparency mode, compared with TI without transparency and standard 3D rendering, in terms of ability to recognize anatomy (respective scores: 4.5 ± 1.1 vs 4.1 ± 1.1 vs 3.6 ± 1.1, P < .05), ability to identify pathology (4.1 ± 1.1 vs 3.9 ± 1.2 vs 3.3 ± 1, P < .05), depth perception (4.6 ± 0.7 vs 4.1 ± 0.8 vs 3.2 ± 1.0, P < .05), and border delineation (4.6 ± 0.8 vs 4.1 ± 1.0 vs 3.1 ± 1.1, P < .05).Conclusions: The addition of the transparency mode to TI rendering significantly improves the diagnostic and clinical utility of 3D echocardiography and has the potential to markedly enhance echocardiographic guidance of cardiac structural interventions.