The aim of this study was to investigate whether there is a reduction in radiation dose and improvement in image quality of pediatric cardiac computed tomography scans performed using the high-pitch spiral technique on a new third-generation dual-source 2 × 192-slice scanner (group B) compared with scans performed using the sequential technique on a single-source 256-slice scanner (group A). We performed a retrospective observational study on 40 patients aged ≤18 years who underwent prospectively electrocardiogram-triggered cardiac computed tomography. Image quality was assessed by pre-defined objective indices and a four-point subjective score. Apart from a higher mean heart rate in group A (P = 0.016), there were otherwise no significant inter-group differences in patient characteristics. The median effective dose was 4.41 mSv (interquartile range 2.58–5.90 mSv) in group A and 0.52 mSv (interquartile range 0.39–0.59 mSv) in group B (P < 0.001), representing a 88 % reduction. Subjective image quality score was significantly better in group B (4 = excellent with no artifact, mode 57.1 %) than in group A (3 = good with mild artifact, mode 57.9 %) (P < 0.001). Noise index, signal-to-noise ratio and contrast-to-noise ratio between both groups were not statistically significant. New third-generation dual-source high-pitch spiral scan technique can deliver excellent image quality with low radiation dose. Our results suggest that it should be considered as a first-choice technique for performing cardiac computed tomography in the pediatric population.