The aim of this study was the comparison of image quality, diagnostic accuracy and radiation dose of ECG-gated volume scan mode of 320-detector row CT with 64-detector row CT. A hundred and twenty patients receiving coronary artery CT angiography (CTA) were divided into two groups. Sixty patients in Group A underwent 64-detector row CTA; for the remainder, Group B, 320-detector row CT was used. Conventional coronary angiography was then performed in all patients. In Group B, patients with a pulse <65 beat/min underwent a prospective ECG-gated volume scan using a 70-80% R-R phase window and 1-beat, whereas a 30-80% R-R phase window, 2-beat CT was performed in patients with a pulse >65 beat/min. In Group A, 247 vessels and 920 segments were assessed; in Group B, 242 and 906. In 320-detector row CTA, the coronary stenosis diagnosis' specificities were 98%, 96%, and 95% at the segmental, vessel, and patient levels, respectively (98%, 94%, and 92% in 64-detector row CTA); the negative predictive values were 99%, 98%, and 100% (98%, 97%, and 95% in 64-detector row CTA). There was no significant difference in specificity or negative predictive values between the groups. The average effective radiation dose in Group B was lower than in Group A (P<0.001). In Group B, the dose for 48 patients with 70-80% R-R phase window, 1-beat scan, was lower than for the remaining 12 patients (30-80% R-R phase window, 2-beat) (P<0.001). The 320-detector CT reduces the radiation exposure by approximately 80% compared with 64-detector CT, with similar diagnostic accuracy and image quality.