Currently 64-multislice computed tomography (MSCT) scanners are the most widely used devices allowing low radiation dose coronary CT angiography (CCTA) with prospective ECG triggering. Latest 128-slice dual-source CT (DSCT) scanners offer prospective high-pitch spiral acquisition covering the heart during one single beat. We compared radiation dose and image quality from prospective 64-MSCT versus high-pitch spiral 128-slice DSCT scanning, as such data is lacking. CCTA of 50 consecutive patients undergoing 128-DSCT (2 × 64 × 0.6 mm collimation, 0.28 s rotation time, 3.4 pitch, 100-120 kV tube voltage and 320 mAs tube current-time product) were compared to CCTA of 50 heart rate (HR) and BMI matched patients undergoing 64-MSCT (64 × 0.625 mm collimation, 0.35 s rotation time, 100-120 kV tube voltage and 400-650 mA tube current). Image quality was rated on a 4-point scale by two independent cardiac imaging physicians (1 = excellent to 4 = non-diagnostic). Of 710 coronary segments assessed on 128-DSCT, 216 (30.4%) achieved an image quality score 1 excellent, 400 (56.3%) score 2, 76 (10.7%) score 3 and 18 (2.6%) score 4 (non-diagnostic). Of 737 coronary segments evaluated on 64-MSCT 271 (36.8%) had an image quality score of 1, 327 (44.4%) 2, 110 (14.9%) score 3, and 29 (3.9%) segments score 4. Average image quality score for both scanners was similar (P = 0.641). The mean heart rate during scanning was 58.7 ± 5.6 bpm on 128-DSCT and 59.0 ± 5.6 bpm on 64-MSCT, respectively. Mean effective radiation dose was 1.0 ± 0.2 mSv for 128-DSCT and 1.7 ± 0.6 mSv for 64-MSCT (P < 0.001). 128-DSCT with high-pitch spiral mode allows CCTA acquisition with reduced radiation dose at maintained image quality compared to 64-MSCT.