Background <p>Anti-scatter grids are commonly used for cardiac catheterization in children with heart disease. However, the effect of the grid on the radiation dose or image quality has not been sufficiently demonstrated.</p> Objective <p>To investigate the effect of the removal of an anti-scatter grid on radiation dose and image quality in phantom and clinical settings.</p> Materials and methods <p>This research consists of a preliminary study using a manufactured phantom simulating a newborn’s chest thickness and a clinical study of 30 infants with simple congenital heart disease. We evaluated the exposure dose by dose area product (DAP), air kerma (AK), and image quality using visual and physical assessments.</p> Results <p>In the phantom study, removal of the anti-scatter grid decreased DAP and AK by 25.0% to 55.6%. In the clinical study, the DAP (sum) and AK (sum) without an anti-scatter grid were significantly lower than with the grid (1.22±0.58 Gy·cm² vs. 1.83±0.64 Gy·cm², <i>P</i>=0.01; 16.22±6.98 mGy vs. 23.23±8.33 mGy, <i>P</i>=0.02, respectively). In fluoroscopy mode without an anti-scatter grid, longer source-image-distances improved the contrast-to-noise ratio for guidewires and angiographic catheters. The accuracy of the examination was not affected in the clinical setting.</p> Conclusions <p>The removal of the anti-scatter grid did not affect the accuracy of the examination and achieved a lower radiation dose in both phantom and clinical studies. Cardiac catheterization without an anti-scatter grid may be a beneficial option for small patients with simple congenital heart disease.</p> Graphical Abstract <p></p>